bingo wings, n. — Green’s Dictionary of Slang

bingo wings n.

[the image of an old lady waving her arm to signal a ‘full house’ in a bingo hall; but also var. on batwing n. (5)]

upper arm flab.

2002		Guardian G2 28 June 5: Tuesday was the usual trip to the gym, to work on the ‘bingo wings’ — the attractive upper-arm bit that wobbles when old ladies wave and shout for a full house.
2009		Observer 1 Feb. 11/2: This ‘better a tumour than a bingo wing’ attitude.
2017		T. Spicer Good Girl Stripped Bare 173: I didn’t turn on the news tonight to see exposed flesh. Why don’t you women cover your arms? It is most undignified. (And this was before the bingo wings.).
2023		Twitter 30 May 🌐 What idiot called them bingo wings instead of rubbery underarms?