I have a few.
1. After the movie "Waiting" came out, a few of the guys at work decided it would be fun to play the penis showing game. I saw Tyler's balls a few times, he saw mine too. Anyway, I was sent into the basement to find out why the water heater was leaking. I walked halfway down the stairs, where I could see almost the whole room, and then I realized the water heater wasn't down there. I was just about to head back up the stairs when I heard someone clear their throat. I looked up to see Tyler, with his pants around his ankles, bent over, showing me "The Goat" as he had pushed his balls out between his legs. I can't get that image out of my mind.
2. Since I worked in an auto shop at the time, we always had some carb cleaner, or starting fluid on hand. It was fun to wait outside the bathroom door, up against the wall. When someone was exiting, they would step out into a cloud of fire. That game quickly evolved to early arrival to work so you could get the person first thing in the morning, as they walked in the back door. Then we were crawling under cars so we could flame on each other's legs. I waited under a car for like 10 minutes to get one of my coworkers.
3. One of my personal favorites was when someone was installing a rebuilt engine, or had just finished rebuilding one, to hide under the car for the initial startup. Let it run a few minutes, then start beating on the oil pan with a ratchet handle or something. Do it at a pace that is consistent with a rod knocking. They shut it off so fast, I love it.
4. My brother likes to have a coworker tell the new guy to ask him how his sister swims. It goes something like this.
Coworker, "Ask Bobby how his sister swims."
New guy, "No, I don't even know him"
"He's really proud of her, she is on the High School swim team, it'll be a good way to break the ice."
"Okay."
"Hey Bobby, I hear your sister is a great swimmer"
Bobby, "You little motherf**ker, I'm gonna kick your a$$, my sister drowned 6 months ago!"
"I'm sorry, I didn't....... Henry said.... I'm....."
LOL, I haven't tried it yet, but I'm gonna.