A CONKER / HALLOWEEN PRANK
This one is always fun. The conker season is also very conveniently coincides with the shops stocking up on their Halloween wares. Most shops will have some form of eyeball balls which fit very well into the shell of the conkers. A lot of fun (for the prankster) to secrete an eyeball into the shell and then let the prank victim open it! You can see our full list here: Top Things To Do With Conkers