When someone smells something gross and says, "ugh, nasty! Do you smell that?" and you breathe deeply to take in the smell and confirm said nastiness, you have just performed a courtesy sniff.
George: Gross, I think the cat peed on my rug. Paul, will you come give it a courtesy sniff?
Paul: (bends face towards rug and breathes in) Dude, yeah, cat totally peed on your rug. Sorry, bro.
Paul: (bends face towards rug and breathes in) Dude, yeah, cat totally peed on your rug. Sorry, bro.
by pseudonym jr August 26, 2011
by mike9 March 07, 2007