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(noun) excessively large breast implants. Usually referenced as such when they are paired with revealing and tight fitting support clothing that pushes them up and out to cause them to form a nearly flat surface on top.

Most prevalent with larger women that choose to get DD+ breast implants to compensate/compliment their fuller figure.
"She is dumb as a box of rocks, but she is redeemed by the stunt bags (she has)."

"With hips like those, she could really use a pair of stunt bags to round out her figure."
by Mark in San Bruno August 15, 2012
someone who doesnt follow through with plans
"jason is a stuntbag because he didnt hang out wit me tonight"
by Ms top notch February 26, 2009