Schrödinger's crabs

Schrödinger's crabs means, you can't have an STD/STI without getting tested.

Do you have an STD? I don't know. Schrödinger's crabs.
Have you gotten tested? I don't want to know, Schrödinger's crabs.

Knee lunch

This is when you get on your knees and eat somebody’s crotch out.

What’re you having? Knee lunch hopefully