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When a woman (usually with big breasts) can make them move at will. It can be extremely sexy, is often done as a party trick (or to try to seduce a guy) in a low-cut top, and hypnotizes all straight guys.

For some women, only the pec muscles move and the boobs jiggle a bit, but on the most impressive boob flexers, the entire breast can lift up and "wave" from the bottom. It can be done one breast at a time, both at the same time, or alternating.

Women in the 18-30 age group can often be seen boob flexing to music to keep the beat. Some can do the move extremely fast. Sometimes women do it subconsciously.

Boob flexing is more impressive than a guy flexing his pecs, especially when a woman's breasts are large. Big, perky breasts actually seem to be more easily flexed and in fact can often appear to defy gravity despite weighing several pounds.

It has become a very popular performance trick in the last decade, probably because a lot if women work out with weights these days. How it got into mainstream culture is debatable but it appears it was first seen on MTV in the Room Raiders" show in the early 2000s. It has also been seen around that time on the show "Blind Date". There are tons of youtube videos.

This move is often performed along with booty twerking. Most likely, the fact that so many women workout with weights as time goes on, has a lot to do with the fact that more and more women can flex their boobs at will.
Did you see that girl's boob flex? It jumped up while she was talking with me. She must like me.
by Big Man on Campus 2 April 17, 2014
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