One of my favorites..
 

Billy and his grandfather are fishing their local lake on a hot Sunday afternoon. After a couple of hours pass the grandfather cracks open a beer and takes a big sip.

Billy : Grandpa, you think I could have a sip of that?
Grandpa : Billy, let me ask you a question. Is your peter long enough to touch your butthole?
Billy : Why, no, grandpa.
Grandpa : When it is, let me know and we'll split a whole case of beer.

Another hour goes by with grandpa drinking beer.. and then he lights up a cigar.

Billy : You think I could have one of those grandpa?
Grandpa : Is your peter long enough to touch your butthole yet?
Billy? No.
Grandpa : When it is you and I will share a stogie together, Billy.

Another hour goes by. Billy starts feeling a little hungry and takes out the sandwich his mom packed for him.

Grandpa : Say, Billy, that looks pretty tasty. You think I could have a bite?
Billy : Well, grandpa.. is your peter long enough to touch your butthole?
Grandpa : Why, yes. Yes it is, Billy.
Billy : Great. Go fuck yourself, grandpa.

That was really funny

I didn't see that one coming -- Great ending! ;)

That is a winner. Great joke.

hahaha....omg that was great!!!