Carp
Carp

A troll who jumps into a conversation without understanding the original topic and going completely off topic from the original intent of a statement. The person can also be described as performing the act of carping.

Where a Troll is derived from the act of trolling for fish, a carp is is derived from the Asian Carp jumping into the boat on their own.
I blogged a piece on how people's backgrounds influence their decisions but a carp showed up and went completely off topic.