Originated in 1805 at the Battle of Trafalgar. Admiral Lord Nelson, only minutes away from trashing Napoleon's grand fleet, managed to get himself shot. As he lay dying, he tried to whisper something to his buddy Hardy. But since he was dying all he could say was Ha...Ha...
Lord Nelson: Liek, OMG I got shot! Ha-Ha!
Hardy: OMG he almost arksed me to kiss him.
Bystanders: OMG OMG!!!
Hardy: HA-HA!
Slang term for defication. Though the reasoning for calling a bowel movement a "ha ha" is generally unknown, it is speculated that the reason invovles the comic value of pooping.