Don't forget such clssics as;
pulling someones chair back as they sit down..ouch,

Having a friend push him backward as you kneel in a ball behind him...teamwork!

De-Bag him..i.e..aproach quietly from behind and pull his trousers down...Takes some practice to get the technique just right!! Is possible to remove both trouser and underwear in one fell swoop...Perform this while he is talking to girls.

put a drawing pin on his chair...vintage 1

Spit ball him from long range and pretend it wasn't you...repeat this till he is so angry you laugh..

Give him a "granddad" i.e.. approach him silently from behind and "Hook" punch him in the sweetspot of his thigh and watch him hobble like an old man!!

Snipe him from LONG range with an air rifle...a real winner..[never reveal your position!]

Destroy some of his art work....if it's on display etc...

some old classics to get you off the ground;]