Onlintrovert
Someone who seems like an introvert online, but is actually an extrovert in real life.
Person 1: I never see him online. Dude never posts anything, barely ever messages. He is probably a bit introverted, isn't he?
Person 2: Oh no he's an onlintrovert. Wait till you meet him in real life.
Person 2: Oh no he's an onlintrovert. Wait till you meet him in real life.