Shit in a Lift
A person who completely dominates a conversation or proceedings, like finding a shit in a lift. No one in that lift is going to be talking about anything else.
Person A: "Man, I hate going to meetings with him. He never lets you talk. He swore he was just going to sit and listen."
Person B: "Yeah, he's a real shit in a lift"
Person B: "Yeah, he's a real shit in a lift"