Smarmily refers to the act of being excessively flattering or insincere. Because it's a specific word, many people might not know the synonyms for it. However, there are many words that can be used in its stead. Insincerely, unctuously, oily, sycophantically, ingratiatingly, and obsequiously are a few options. Insincere is a great synonym because they both refer to someone presenting themselves one way when they don't mean it. All of these words can be used when referring to someone who is trying to manipulate a person or situation through flattery or false kindness. Using synonyms can help avoid repeating the same word in writing or speech and can also broaden your vocabulary.