2 tramps walking down an alley:
Tramp 1. "Have you shit your pants?"
Tramp 2. "No i haven't!"
1. "Are you sure?"
2. "Yes!!"
100 yards further down street: 1."Are you sure you haven't shit? It fucking stinks."
2. "Yes I'm sure!"
1. "Fuck off, let me see."
So the 2nd tramp pulls his trousers down and there's shite everywhere. Up his back, all over both cheeks, down the back of his legs. 1st tramp says "I thought you said you hadn't shit yourself??"
2nd tramp replies "I thought you meant TODAY??"