To express on AIM when something was funny, because just 'haha' isn't that dramatic and can be used as just aknowledging when someone has said something.
Bobby31: ...they call it cheese and quackers!
Annette85: haha Bobby31: oh come on it was funnier than that
Annette85: hahaha
When someone starts laughing really hard and they feel the need to slap the nearest person. Then when the person got slapped asks why they did that, they say it's a joke.
Friend 1: omg that was so funny Friend 2: hahahaha *slap*
Friend 1: ouch what was that for
Friend 2: chilllllllll it was a joke