1) When you want to sniff your pits but you want to do it discreetly you lift your arm and pretend you are scratching your nose with your shoulder, but at the same time you are "Sniff Swipe"ing.
2) Pretending to scratch ones nose with your fingers after touching something.

phone: why don’t you go to sleep tommy it’s 2 in the morning?
tommy:why don’t you die you dumbazz