That is pretty darn funny! I had to laugh on that one :D

type in 10 dollars in the scratchpad and hit a button and have a 10 dollar bill partially coming out of the acars printer...let the F/A think i's an ATM ....she might ask for some money on the last flight for an overnight to a totally new crew.

By the way, just a friendly reminder to the new guys, do not try to play a prank on a fellow f/a unless you know him/her really well. Don't forget you're on probation for a year, you're not a permanent employee until you're off probation.

I dunno if this has been said already, but:
If you are on a single F/A aircraft, switch over to PA when the F/A is doing his/her safety announcement and make comments over it when the F/A pauses from speaking to demonstrate...
IE "Ohhhh, so thats how you do it" when they are demonstrating the seat belts.