According to the Oxford English Dictionary editors, mansplaining is “to explain something to someone, typically a man to woman, in a manner regarded as condescending or patronizing” (Steinmetz, 2014). read more
Based on your description, this isn't sexist. It's being a jerk. Jerks do this to women. They also do it to men as well. read more
When women and men get together, things can get interesting. A man may mention something he knows in order to establish his status, while a woman will acknowledge his point to make a connection. The man, meanwhile, will take this to mean she accepts his status, which may prompt him to launch into the dreaded mansplaining. read more