Crump

When you're doing it doggystyle and the person on the bottom farts (pumps).

"We were having sex and he/she crumped during it"
"Did you just Crump?"

Crump

Verb: When you fart whilst being fucked from behind

The past tense is crumped

"We went back to mine and during sex he/she Crumped."
"Did you crump during sex"