A sniffer, also commonly referred to as an "ass kisser," is one whom, basically, can't leave a person alone. A sniffer, will perform such actions as, following one around, calling or texting someone to almost no end, over complimenting a person to gain one's attention, and paying frequently unexpected visits to one's home.
Sniffers can be commonly noticed at parties, events, family functions, in the work environment, and most social gatherings.
Did you go to Dad's house party? There sure were a lot of sniffers that wouldn't leave him alone.