A person whose lack of skill and knowledge in a particular field do not stop him/her from participating and commenting extensively in and on that area. Boomheads litter most poker tables and can be identified by their thick verbal effluent. Salespersons are usually boomheads. All boomheads blow up in the end.
Ed: Dude, Murray's been telling me to put all my money in Bear Stearns stocks. He says I can't lose.
Al: Don't listen to Murray. He's a boomhead.