Snape was now aware of Harry's intellect, and even after his stunt at the Opening Ceremony, they had still underestimated the cunning and guile the supposed ignorant child had. He had expected to easily cower the snivelling child but had instead made himself look like a fool with his inability to punish the brat. Thanks to Dumbledore's insistence to wait and see how the boy reacts, his reputation was now in tatters!
'Well, you old fool, his reaction was to blackmail me with the threat of ruining my life! You can't blame me for taking a more direct approach.' Snape thought to himself, a green child was no match for a professional wizard!
"You talk a good game, Potter, but in the end, you are still a silly little child trying to play with the grown-ups. You voluntarily meet me in secret and then proceed to threaten to ruin my life. What if I just decided to wipe your memory or force you to drink a loyalty potion? After all, you repeatedly call me a Death Eater, what is to stop me acting like one?"
Harry looked at the sneering, greasy-haired emo and gave him a derisive snort. His goal was to force Snape to use Legilimency so he could capture his mental avatar. Snape's Occlumency defence was to hide his important thoughts and memories behind a shield of other fake or worthless memories.
Harry could easily just continue destroying the memories Snape used as a shield, but he was afraid of wiping out something useful. After all, the man for all his many, many faults was an accomplished potions master. Harry wanted those memories for himself, so he didn't need to learn why stirring a cauldron clockwise would make a potion explode instead of anti-clockwise to produce a cure for a laxative or something.
"As I mentioned before, Madam Bones was kind enough to give me a way to contact her if I was in trouble. I have a friend that will summon her if he doesn't hear from me in thirty minutes. Plus, you are only a potions teacher, you probably needed the help of your Death Eater friends to hold down women as you r*ped them because you couldn't even cast a spell to clean your hair! You know the old saying: he who can, does; he who cannot, teaches."
Harry then laughed in Snape's face after mocking him, the man's grimace of displeasure only making him laugh harder. For all of Snape's supposed mastery over the mind arts, he was easily riled up by insults to his magical proficiency. Probably having to do with his unresolved childhood issues and having to watch the girl he obsessed over pick his tormentor over him.
Any restraint Snape had that was stopping him mind raping Harry was immediately destroyed when he heard the little shit so crudely slander him. Knowing he needed to act fast if the child's threats of Aurors were genuine, he decided to read his mind to find the best way to handle this precarious situation.
"Legilimens!" Snape coldly spoke as he used his magic to force his way into what he thought was an unprotected mind.
Harry smiled as he felt the intrusion into his mindscape and entered into his vault to watch how Snape would deal with futuristic weaponry. Pretty well as it turned out. After the initial surprise of finding himself in a post-apocalyptic town instead of sifting through jumbled memories, Snape had his wand out ready to defend himself.
After trying to retreat back to his own mind and finding a barrier preventing him from leaving, Snape could only go with his original plan of subjugating the child's mind. He could have put his full mental strength into forcing his way through, but that would leave himself open to an attack. Harry was not about to let him escape after provoking the Potions teacher into invading his mind in the first place. Home field advantage was actually a real thing in mind magic.
Harry launched a few weak raids of ghouls and raiders to make it seem like he was actively trying to attack Snape and defend the raider base. He wanted to lure Snape in enough so there would be no chance of escape. If Snape had put all his effort into retreating, then the most Harry would have been able to do was give him a crippling blow before having to invade Snape's mind to finish him off.
This way, he could cut this piece of invading soul off and scan it for all of his memories. He doubted Snape was skilled or paranoid enough to limit the memories of his mental avatar before attacking. The lasers and bullets only stumped Snape once before he adapted his shields to stop both, and his cautious advance only saw him receive a few wounds.
Harry had to give him credit, although the man was an absolute f*ckwit, he knew his way around spellwork. The Sectumsempra Curse was invented by him when he was still in Hogwarts after all, and his love for the dark arts had supplied him with many inventive spells to be used on the poor raiders.
After half an hour in the mindscape, the raider base was littered with enough gore to make a horror movie look like a comedy. Snape was not averse to slaughtering his way through Harry's mental defences, showing his experience in killing humans with magic. But by the time he reached the decoy computer that should have been Harry's mental core, the raider base had been surrounded by the real enemies that would make those Snape had already defeated seem like a warm-up.
"Thanks for playing along Snivellus, I was worried that once you saw that I knew Occlumency, you would do everything you could to escape. Now you have no chance to leave. Wow, you haven't looked this miserable since you saw me walking around outside the house Voldemort attacked! Cheer up, you will soon have a new master to follow!" Harry mocked the panicked Professor at seeing his current predicament.
"How do you know I was there?" Snape shouted out in disbelief, completely forgetting about the Snivellus insult in his shock. Harry had only been a year and a half when he was orphaned after all.
"Oh, you unfortunate idiot, I will return your earlier words back at you. 'You are just a silly little child trying to play with the grown-ups'. My mind has been fully developed since Voldemort hit me with the Killing Curse. I remember everything from the night your Master killed my parents.
He also made the mistake of leaving a juicy piece of his soul behind for me to extract all of his memories. I know it was you that supplied Voldemort with half of the prophecy that ended up directing him at me. Even your begging to spare my mum for your sick desires was there for me to discover."
"No! No, it was an accident, I didn't mean to! I loved Lily!" Snape cried out in horror at the implications of this shocking news.
"Hahaha, you are pathetic! You claimed to love my mother but didn't even warn her of Voldemort's plan to kill her husband and child! Even if you hated James Potter, that does not excuse you for watching on as Voldemort tried to kill her innocent child!"
"No, I went straight to Dumbledore and warned him! He assured me he would keep her safe!" Snape was visibly distraught while shouting out justifications for his most painful mistakes.
Harry couldn't help it, he laughed even harder at the thought of Snape grovelling to Dark Lord Dumbledore to protect Lily while he plotted to kill her even as he made Snape swear a binding oath.
"You really are a dunderhead! Albus Percival Wulfric Brian Dumbledore is the greatest Dark Lord of our age, and you swore yourself to his service even as he plotted the death of the only person you ever loved! It is really too funny!"
"W-what do you mean? Dumbledore is the Leader of the Light!" Snape said in mounting horror, any semblance of dignity or composure now completely gone.
"Tom Marvolo Riddle, aka Voldemort, was just a pawn created by Dumbledore to increase his reputation after he betrayed Grindlewald for the Death Stick and fame. Do you honestly think he would have interviewed a drunken incompetent witch for the outdated Divination role in the Hog's Head Inn?
Aberforth hates his brother with a passion for killing their sister, and you think that Albus just decided to use his brother's Inn for an interview? When Hogwarts is right next door and all other meetings are conducted there?
You actually think that it was your good luck to 'stumble' into a 'true' prophecy occurring just at the right time so you could report it back to Voldemort? I have no idea if he orchestrated the prophecy as well as the situation, but do you think he was incapable of putting up a privacy charm?
You poor gullible fool, just like the puppet Voldemort, you have been dancing to the old man's tune since you were a first-year student at Hogwarts!"
And then Harry proceeded to laugh as Snape fell to his knees, crippled with hysteria at the sudden knowledge of the machinations he was a victim of. The loudspeakers echoing Harry's mocking laugh to directly pierce through Snape's willpower. The troops surrounding the raider base didn't even need to attack as Snape faded away as his mental discipline was destroyed by the news that his whole life was a lie.
The bundle of hate, depression, sadness and bitterness that was Snape was defeated without even a grand showdown. His insecurities and unresolved emotional issues ended up destroying his usual superb mental discipline. But Harry always suspected that Snape was just another fool that thought he was a Master Occlumens.
Occlumency was mastering your emotions, not just bottling them up behind a cold exterior. If Snape was a Jedi, he would be as shit as Anakin Skywalker.