When a person farts while receiving oral sex, it's called a
chin-up.
The word actually comes from the reaction of the person giving the oral sex at the moment of the fart;
the first thing most everyone does is lift their
chin up to look at the foul person with disgust. This is usually followed by a break-up or the disgusted person leaving in a hurry.
"What's wrong, Jimmy?"
"I had to break up with Christina last night."
"Why did you break up with her? I thought things were going so well."
"The wretched woman gave me a damn
chin-up last night when I was going down on her."
"Can't say I blame ya, Jimbo .....
keep your chin up though.... there are
plenty of fish in the sea!"
"Not funny man .... not at all."