During sex I fantasize that I'm someone else.

Framed as a self-deprecating one-liner, the joke turns on Richard Lewis’s trademark persona of anxious, dissatisfied self-scrutiny. By claiming he fantasizes he is “someone else” during sex, the speaker implies a level of insecurity so extreme that even intimacy becomes an occasion for self-escape. The humor comes from exaggeration and incongruity: sexual fantasy is usually about desiring another person, but here it is redirected inward as a wish to be a different self. Read more broadly, it satirizes modern identity anxiety and the pressure to perform—suggesting that shame and self-comparison can intrude even into private pleasure.