An individual who is always clueless.
Ricky is on third base. The ball has been hit. Ricky staring off into space doesn't realize and the team yells run home. He looks around and starts running to his house. Craig looks at Ryan and says, "He is such a Blow Bag."
Someone who constantly self-promotes their own talent, products, or business interests, to the annoyance of everyone around them. Usually an artist or musician, but sometimes a booking agent, salesperson, consultant, or other self-employed business-type.
Joe: Dude, did Dave tell you about his band's new CD?
Alan: Did he! He went on for 20 minutes about how it was going to go Platinum within a week. That blowbag!
A girl who likes taking loads of semen inside her
Hey that chick is such a blow bag.. she loved it when i blew inside her
A pack of food which should be vacuum packed but contains trapped air or a hole in the packaging.
Start opening those blowbags.