Hey, look! It's like a cock but smaller
Without a doubt, the most hilarious thing a man can shout from a bathroom stall in a crowded public restroom. "Eye's front and center gentlemen, unless you suspect (for obvious reasons) that the comment is directed towards you".
I was taking a shit in the corner stall of a nearly-packed restroom after the Concert. I could see there was no one in the stall to my left, so I shouted "Hey, look! It's like a cock but smaller". Suddenly, you entire restroom fell silent, and I had to stay in the stall until I could exit with a straight face.