Even though he already expected something like this, Roy was still bothered by these idiots. Not because of the reason, but because of how cliché it felt.
There was nothing wrong with checking a new guy's strength, and especially someone young like him, these guys needed to know whether he had the skills and abilities or not.
It was just that for some reason it felt really chuunibyou-ish and he didn't like it. But it wasn't like he had much of a choice anyway, so he could only go along with it,
"Alright, you two can attack me together!"
"Huh!? Don't take us lightly you brat!"
Roy's words were just like a ridiculous taunt to the two fighters, as he was taking them extremely lightly. He didn't even consider fighting them one after the other, but he wanted both at the same time.
It was the same as saying, I don't need to break a sweat to deal with flies like you. And in reality, he didn't, but those two had no way of knowing that.