People talking in really high, squeaky voices (helium induced or on the radio/tv when they are pretendign to be flies/bees etc)
Dogs walking into things
Cats falling off furniture
Toddlers being furious and pointing and explaining in toddler language just why they are so furious and expecting you to understand.
Babies dressed as bees/pumpkins/christmas puddings
What things never cease to amuse you?