Which reminds me of the day in Torts class in first-year law school, when Professor Harry Kalven was leading a discussion of the principal that certain acts, which would otherwise be improper and tortious, are permissible if done with consent. (For example, punching someone or cutting him with a knife would ordinarily be a tort -- but the former is permitted in a boxing match, and the latter is allowable if you are a surgeon performing surgery.) But as he pointed out, the consent must be an informed one, not a consent given in ignorance or obtained by fraud.

At which point Professor Kalven posed this question: "If you refuse to pay the whore the $25, does it vitiate her prior consent and create a tort?"

To which one student (me) promptly replied, "Professor, where can you find one for $25?"

Brought down the house. Harry and I were great friends from that day to his death.
Note to Jazz-o: this classroom technique should be used only with care!