Under arm flab, or fat. When older women win during Bingo games, they throw their hands in the air saying "I got a bingo!!!", flapping their arms (and underarms) wildly about in their excitement. Thus causing the wind movement from their "bingo flappers" to eradicate all other bingo players, bingo cards. Game, Set, Match.
" How do I get rid of these Bingo Flappers under my arms?"
" That girl has some serious Bingo Flapping going on over there".
"My god honey, Kristie alley has huge bingo flappers. She must be able to fly around the world!"