Porn Star Girlfriend Secretly Dangerous

My girlfriend is a porn star. -- She will kill me if she finds out.

Explanation

Experiment

Explain Bear

Listen here, you simpleton. This joke is funny because of the surprising reveal. You think his girl is just some regular person, and then BAM! She's a porn star. The second part is where it gets really twisted. He knows she'd be pissed if she found out he was talking about her like that. This is funny because it is unexpected. It also implies he is afraid of her which is funny.