When I was 18 years old, I worked at a McDonald's. Oh, how I hated it, but I did manage to have some fun.
Example: When a new cashier was closing the store for the first time, there was a special prank that was always good for a laugh. I present the following in the clean, wholesome spirit of April Fool's Day.
1. Take two or three quarter pound hamburger patties out of the freezer. Put them somewhere in the store where they won't be noticed (a locker in the break room, for instance). Leave them alone for a few hours so they get nice and soft.
2. When the patties are the right consistency, roll them all together into a cylindrical shape. You're going for girth and length. If you do it right, you'll get a "snake" that's between 12-15 inches in length.
3. Being as inconspicuous as possible, cook your prop in the deep fryer. This should take about three minutes or so.
4. Remove from oil; drain. It should look like a big, brown turd.
5. Wait until the store is closed and the manager is in the office counting the drawers. Take the prop into a restroom (your choice) and arrange it in the toilet, preferably with part of it draped over the rim of the bowl.
6. The new cashiers always get stuck with cleaning the restrooms. Wait until she heads in that direction.
Usually, a yelp of disgust will be heard and then the patsy will come running out of the restroom. At that point, you can laugh and explain the trick, but why cut things short? Fortune favors the brave...
If you can keep a straight face, accompany her back to the restroom. "There, there, sweetie. Let's see what the problem is."
Upon arrival, you can play it several different ways. You can purse your lips and say, "Boy, that's disgusting. Unfortunately, you are on bathroom duty..."
Or, you can walk over to the toilet and examine the specimen for a minute or so, then grab it and throw it at the cashier. Some people cry when you execute this maneuver, however.
If you really want to make a lasting impression, however, go the extra mile and prepare a second turd. Keep the extra one safe and clean. When you accompany your victim back to the bathroom, solemnly assure her that you'll take care of the mess and send her out. After a few minutes, walk back up front holding the CLEAN turd. Say something like, "I don't know what all the fuss is about," and then take a bite out of it.
I was never able to go that far, although I did have the second turd all fried up and ready to go. Perhaps someone out there in blog world will pull off this tasteful stunt and succeed where I failed.