put cling film over the toilet
get 1 of them fake winning lottery tickets or scratch cards that say youve won the jackpot haaa my cousin got 1 and was running around screaming 'whoooooooooooooooooooooooooo omgggg ive won ive wonnnnnnn' haaa was well funny
ring 1 of them prank wind up lines and you can listen while some jokester plays a prank i did 1 on my other cousin pretendin there was a warrant out for his arrest looollllllllllllllll
or say something shocking like 'im pregnant' or 'im a lesbian' that may be taking things over the top though depends what you find funny!