A person who is in a deep conversation, and all of the sudden says a random thing, sentence, or thought, that kills the conversation.
Much like a speed bump, it slows you down, and leaves you confused, stranded, and a little freaked out.
Shelly: Hey, so how was your date last night?!
Clara: zomg you'll never guess what James did last night...
Clara:... hmmm... today my dog got a bath. he doesn't like water. you should have seen him squirm! hehe i like dogs! do you like dogs?
Shelly:..... conversation bumper much?!