Most of my funniest memories centre around my grandparents. one time my gran thought it would be funny to throw a cup of water out the bathroom window onto our heads (me, sister and 2 cousins). She failed to realise her false teeth had stuck in the cup, and all we saw was a lower set of dentures flying out the window.
When I was about 16, I was helping my Dad and Grandad load a fallen tree into a trailer to take back to the farm. We didn't have anything to secure it with, so in his deadpan way my Grandad said to me "You sit on top of it and make a noise like a piece of rope". Me and my Dad still laugh about it today.