Years ago in London we had servers that were fond of our homemade chocolate petit fours so I made a batch of them with chocolate Exlax and left them sitting around..... kind of backfired though when we lost 3 servers that shift... but not as much as they backfired.
You take some cardboard, you cut it into the shape of a cutlet, you use a meat tenderizer on it, season it liberally, breadcrumb and fry it then serve it up to the peasants with a nice mushroom demi, they'll never complain about staff food again... trust me
You buy an identical combination lock for someones locker then switch it while they are getting changed at the beginning of shift.


CAUTION: THIS SHOULD ONLY BE USED AS A LAST RESORT (OR FIRST RESPONSE) TO A PRANK PLAYED ON YOU
Purple broccoli used to be really funky in the mid 80's (oh god i'm old) we used to give it to the newbie to cook, always with the lecture about you know what you are doing? this stuff aint cheap! as soon as it hits boiling water it turns green...What the **** happened did you put salt in the water? there is no right answer
Live lobsters.....so many possabilities, my favorate is under the plate cover and into the dishpit
Taking an pigs eyeball into a department head meeting can be considered juvinile... trust me, it did take them some time to notice what was floating in my water glass
Talking of department head meetings if you ever want to speed one up just spend a couple of hours fileting salmon before hand... or during it we're born multitaskers
Telling a newbie that snorting saffron will get you high, actually that one wasn't cool, the bright yellow muccus was disgusting
Having the G.M. run up to you saying you speak Welsh, I want to make a toast to Richard Burton (this was before he died, we didn't serve dead people at the restaurant) this was in the middle of service so I quickly taught him a classic toast that translates to "all English are *****oles" I changed jobs soon after.
Serving a nice rabbit stew then advertizing it on the chalk board as Watership Down Casserole "You've read the book, you've seen the film, now eat the cast" for you young farts google it, it's a classic story, much better than Old Yeller... and tastier too