When you walk into a room (most often the kitchen) and it's disturbingly obvious that someone just opened the trash lid, if only for a second, and let out a gas cloud of nastiness.
Usually this occurs when everybody in your shared apartment thinks it's someone else's job this month to change the kitchen trash bag.
Dude I just walked through the nastiest trash-fart in the kitchen! Who threw something away??
Man I think those girls left your party because I threw away my takeout boxes and the wretched trash-fart almost killed their friend.
If someone doesn't change the trashbag in this bitch soon, we're all gonna die from the trash farts! Whose month is it?
When someone's gas smells like old rotten trash. It is a distinct smell unlike other farts ie. eggfarts, dairyfarts, shitfarts. You literally can smell something rotting away in the culprits intestines. Sometimes, it requires intervention with a shop-vac.
Dude! That was a rancid trashfart! Go check your drawers!