Awkward everyday stories- "I didn't touch your butt"

So today I was waiting to wash my hands during class. This guy was taking his time because we had just been dissecting stuff and there was a line forming. His friend proceeded to run up tapped his ass and ran to his other side.
Guess who was standing right behind him watching the whole thing play out? O.O that was the look he gave me. No joke. His friend was dying of laughter and despite me pointing his friend out he said, "No, it was you!"
Yup... thanks people.