{This is a collection of ways to kill 40K Orks. Some of them are from canon, some from other people, and from me. Enjoy.}
1. Go up to an Ork and tell them the floor is lava.
2. Pretend your hand is a gun and make pew pew sounds(This part is canonical lol)
3. If it's raining tell them that water is an automatic ork killer.
4. Cause mass ork suicide by telling them that eating dirt will give them the most painful and Gory death so that an entire WAGH would start eating the ground and become a sea of blood and guts.