Someone who is always taking over a conversation that they were not originally part of. The person is within earshot when you start a conversation, then as the conversation is commencing, the third party loudly interjects a comment designed to derail the conversation so that all attention is then upon them. Usually they follow this up with even louder and more outrageous jibberish.
Frank: So, Chuck what did you do this weekend?
Chuck: Saturday night was awesome, I banged two chicks at once!
Curt, sitting just within listening distance, prepares to board the conversation just like a pirate boarding and looting a ship on the open seas, yells: I banged twelve chicks once!
Curt: But I got syphilis....
Curt: I gave it to Hank last night.
Frank: Curt is such a Conversation Pirate!