Hit and Run

I'm looking for a word. I want to describe the person who, as soon he he sees you in a social setting, makes a beeline for you, cuts in on your conversation, and drives the other people you were talking to away. This person is awkward and a linger-er, so maybe he's an 'awkwalinger'. They don't know when to move on. And they're trying to fill their need for validation by sucking the life out of you.

They need to learn the hit and run method. Come in, say hello, and keep it moving! This happened to me last week. I was having a good conversation with someone I really wanted to talk to, until I got ambushed by this dude, who demanded my attention and drove my friend away.