A friend kept trying to steal my sushi off my plate at a sushi restaurant.
So while she wasn't looking I stuffed it full of wasabi, put a bit of fish back on top to cover my tracks, and pretended to not be looking when she started reaching towards it.
She tossed it into her mouth, started chewing down, and I just swung my head towards her to say "you f****d up"
5 minutes of coughing, muffled screaming, and copious amounts of water later, she had learnt her lesson.