Two guys are fishing from a riverbank. One of them says "Excuse me, I'll be right back" . . . and disappears into the woods.
A few minutes later, he returns and continues fishing.
About a half-hour later, this happens again. A bunch of times.
Eventually, his buddy, curious, asks "I don't mean to be nosy -- but why do you keep disappearing like that?"
The first guy replies, "I have a case of diarrhea."
His buddy says "Well, why didn't you tell me? I'd a helped you drink it."