Nothing.
It's just the way that everyone was laughing that made it so funny.
But, I suppose if you think about it, it's like saying you have pee in your colon. But that's not really funny.
colon hyphen P, aka :-P is basically a funny face sideways. The colon are the eyes, the hyphen is the nose and the P is the mouth with its tongue sticking out.
the equal sign or the colon or a semi colon with a p or a parenthesis :) :p ;) ;p =)
colon plus capital P - :P
colon plus capital P - :P
In a business letter =P
125500....:P
YES! :P
purple
You need to be funny :P
They were very funny! :P nahhh thoo! :P
Funny faces! :] ;} :P ;P
preposterous