conversation pouncer
Someone who lies in wait with a keen eye for someone who is about to leave, taking the opportunity to pounce and force a conversation upon his/her prey.
I’m leaving the office now, I am going to army crawl to the door so I don’t get snatched by the conversation pouncer, if you don’t hear from me in 15 minutes, please start a fire in the building so I can be released from the jaws of this predator.