I don't like it either, but it seems to be the approved "phrase" at ds's school. Anyone doing a trump fart is then expected to say "pardon me" which I also detest. ("sorry" or "excuse me" is what we use at home).
In my family (the one I grew up in), we played Trumps. Card game, a bit like Whist.
Dh insists on trump for fart. It is now ds's favourite word, dd is a little past this phrase but does like a good passing of wind. Cue much hilarity at family gatherings when someone suggests "game of Trumps anyone?"