Smarmy describes someone who is overly flattering and fake. A smarmy student might tell a teacher, "You're looking even more lovely than usual today," with a big smile.
Smarmy describes someone who goes way over the top trying to be suave and charming — fooling no one. A smarmy car salesman will compliment your outfit and your hair and your taste in cars, always with an unpleasant falseness. In the 1930s, smarm was a verb that described smearing the hair with pomade, which makes it look shiny and slick. Back then, smarm also meant smearing with flattery.