Do you know the difference between toilet paper and a shower curtain?
So you're the one!
This is a setup where the punchline is unexpected. The joke leads you to think about a practical difference, but then it accuses the listener of being the one who uses the shower curtain as toilet paper, which is disgusting and unexpected.
Tyler
Why did the chicken cross the road
To get to the other side
ANoNyMoUs
Tyler, you need to get a life.
joe
curtan