Commonly when used to define the
father / fathers of inbred
people. These men often have no sexual standards and will do just about anything for a shag, even if that means going for their sisters / cousins.
May also commonly be used in replace of haha when someone's fingers are too chode like to properly type on their keyboard. It is a sign that you, yourself are small and are not able to grow above 5ft 2".
(David) Hey
Chris, did you know John's dad is married to his sister?
(
Chris) apapapapapa you're joking, right?
(
Chris) Oops, I meant hahahahaha!
(David) No, his dad is an apapapapapa.