mouth burglar

Mouth Burglar
n. A person who steals a thought or idea, soon after it's initially said by someone else, and make it your own.

Mouth Burgle
v. The act of stealing a thought or idea. Most commonly used in the past tense.

n. You fucking mouth burglar, that was my idea!
v. That summumabitch stole my idea. I've been mouth burgled!