Someone who interrupts a conversation with the opposite sex or same sex and start a new conversation. Also know as convo blocker
I was talking to this girl and he came and started a whole different conversation with her. He is such a conversation blocker
People that consistently sit close to conversations but refuse to let the conversation flow down the table. For instance you have to lean into the middle of the table to talk.
Wow I can't talk to Jack because Kevin Murray is a giant conversation blocker.