Practical jokes to play on people

[A.J.M]

A close friend works for one of those outdoor activity centres, and during the weekend she and a few others started playing some minor practical jokes on the leaders for a bit of fun.

The leaders also joined in back and a good laugh was had, but i think the leaders got a bit annoyed that they could'nt come back with decent ideas and gave them all a row over it.

Shes asked me for some ideas to have one last go at it before calling time on the idea before christmas holidays.

I have a few but i think the collective silly mindedness on here should gain a few more.

So reminding she works at an outdoor centre and can get access to some unusual stuff, lets have your idea's.

Random and silly/rude are all welcome

[TheEnd]

chafe some ropes?

swap sugar for salt and vice versa

this really is a broad field...
narrow it down a bit, what were the last few things done?