When you're having sex ( mish, doggy, cowgirl etc) you pull out and fart in her face, then continue as if nothing happened.
Last night when I fucking my girlfriend, I did a Dirty Chris in her face.
A sex act in which the dominant partner spits and hacks up loogies on the submissive partner. Especially popular among practitioners of sadomasochism.
He likes the dominatrix to perform the dirty chris on him whenever he's in town for the weekend.