When 2 or more people engage in a contest involving their farts. The goal of the contest is to either produce the most consistent, loudest, or perhaps heaviest fart capable of a normal human being.
"Oh man, me and my brother got into a fartgument last night, it was pretty bad."
The sigh of relieve and that sillysmile a person has after letting out that gas that has been held in for so long.
Slightly changed term from 'Testees' Ssn1 when Peter lets out a huge fart that he thought was a baby and Ron tells him he's got post-fartum depression. Post-fartum expression is easier to relate to.