user
Given a cartoon image and a caption. Caption: I have to warn you, I don't exactly have a bladder of steel. Question: Generating an explanation of why this image/caption combination is funny. Answer: 
assistant
People on window seats in airplanes need to climb over people in aisle seats in order to access the bathroom at the end of the plane: this can be annoying because of how cramped the space is. Here, superman, also known as "the man of steel" is warning his seat-mate that he will need to get up to use the restroom because, despite his name, he doesn't have a "bladder of steel," i.e., he will need to use the bathroom to pee frequently.