Ever since Audience Participation became an integral part of showings of The Rocky Horror Picture Show, the funniest parts of a performance are usually audience members shouting out something that changes the meaning of the subsequent line in the movie. Perhaps the best example is where Frank says the word "spark" in an especially dramatic way, in a British accent with the "r" dropped. Result: this line is almost always preempted with "Who gives the best blowjobs on the Enterprise?" or something similar.