i work in a warehouse and quite a few pranks been pulled, some of the older guys have these metal mugs with a screw on top to put there coffe and tea in kinda like a mini thermos so out came the no more nails put it all around the top screwed the lid on and walla no more nails = no more tea and coffe lol they where pis#ed. and i happened to p off one guy real good he went and complained lol he put his pen down so while he wasnt looking i coverd it in clear silicone gel he then picked it up and got covered then to get out of the warehouse you have to push a button so i decided to cover that in gel and told him the boss was outside and wanted to talk so he went pushed the button to go out and walla again gel all over him lol. i happen to be the local prankster at work another one to try, if someone has a drinks bottle i'e filled with water and so on, you make loads of small slits around the top so when they go to drink it it pours all over them always funny could go on but think i wrote a bit to much already