Joe and Tom had been at the bar for a while...

…when Joe said he'd give Tom $20 if he'd take one sip out of a large spittoon at the end of the bar.

Tom: "No way, man. That's disgusting!"
Joe: "What if I offered you $50, then would you do it? Just one sip??"
Tom: "Uh. No. Even for $50, that's just too gross!"
Joe: "Well…what if I offered you $100? C'mon…it's just one sip!"
Tom: "Well…I guess it won't kill me and I really can't turn down that offer."

So…Tom picks up the spittoon to take a sip and keeps on drinking from it…glug…glug…glug…

At this point, Joe is repulsed and says to Tom: "Alright, already! STOP! You're grossing me out. You only had to take ONE sip!!"

Tom promptly empties the spittoon, puts it back on the bar, wipes off his mouth and sits down next to Joe.

Joe: "Why did you do that??? That's was SO disgusting!! The bet was for you to take ONE sip and you drank the whole damn thing!"…to which Tom replied: "I couldn't stop. It was all one piece."