Steve: nothing man... i heard a strange noise and thought i would just check it out....
George: i could see your feet under the door and could hear you breathing asshole!! your such a sniffer!!!
As in, one who attempts to ingratiate himself to a clique of attractive young women, in the hopes that he will copulate.
Then promptly moves to another clique when rejected.
Sniffers can be commonly noticed at parties, events, family functions, in the work environment, and most social gatherings.