1782, "chic; snooty, haughty." Possibly from earlier Scottish noun snifty, "insignificant person" (1660s) but the connection is uncertain.
In mid-19c. became a fashionable word and for a time could be used with no negative connotations.
"Snifty" visiting cards for new years! Come and see 'em! [advertisement in The Wilmingston Post, Dec 25, 1869]
Sense "smelly, odoriferous" is by 1863.