Don't do something stupid or mess up an opportunity.

Variants include: if you see a bunny, don't fuck it; that bunny has been fucked; and fuck the bunny, you should not.

It comes from the anime Sensitive Pornograph, where the main character, a pet-sitter, is given instructions to feed a bunny for his boss, and instead of a rabbit, he finds a man dressed as a bunny bound in his closet. Instead of doing what a sensible person would do and calling the cops, he proceeds to fuck him.
Richard: Hey, man, I've got a date with Sarah this Friday! I think I'm gonna take her to see a Van Damme movie.

Eli: Dude, don't fuck the bunny. Take her to see something with cute animals or shirtless Matthew McConaughey.
by YourNerdyProtagonistGirl August 31, 2012
Get the don't fuck the bunny mug.