TAC-fart

Not to be confused with a tactical fart.

A TAC-fart is the acronym for a "top arse crack" fart. These are specific farts that are funnelled up the arse crack and expell themselves out the top of the trouser band, onto the lower back.

They are often of a high pitched squeaky tone and best performed when sitting on a hard, flat surface where the air has no way to move forward from the anus, thus must escape via the top of the arse crack.

Nice TAC-fart, you could have warned me though my mouth was open.