Smarmy is an adjective which means to act as if you are genteel or well-mannered, but such actions are not credible or believed.
Something can be smarmier than something else, and one can even be the smarmiest. The noun form is smarminess and the adverb form is smarmily.
A smarm is a word or behavior that is smarmy in nature. It is a backformation from the adjective. Outside of the United States smarm is sometimes used as a verb to act in a smarmy way, or to smooth one’s hair with hair product.
Examples
The Coen Brothers’ “Burn After Reading” is a prime example of a film filled with lovable idiots, but here the three central characters are so stupid and smarmy you want to slap them. [The Journal]
Weirdly, Chris Pine comes off rather well as Waltz’s embittered son Rex, perhaps because playing someone who’s smarmy is a better fit for his talents than the straight-up action hero roles his bland good looks have thus far secured him in the wake of Star Trek. [The Scotsman]
It’s a time of year when television watchers can either wallow in an orgy of snark or emblazon that line on a T-shirt and embrace the smarminess. [The New York Times]
But the Cabinet that smarmily welcomed Comrade Li Keqiang is the same one that is always hot to intervene against tyranny and misgovernment in Iraq, Libya and Syria, and which haughtily condemns Russia for annexing Crimea. [Daily Mail]
My own online language-learning may have begun as a transparent attempt to smarm the in-laws, but it’s since become so much more. [The Independent]