The story
Clipping of bimbo + BEM (“Bug-Eyed Monster”) + bum (“incompetent man”). From a typical composition for the cover art of science fiction pulp magazines such as Thrilling Wonder Stories, notably by artists such as Earle K. Bergey and Rudolph Belarski, featuring a woman (the "Bim") being attacked or threatened by a monster (the "BEM"), while a man (the "Bum") protects her and/or attacks the monster.
Etymology from Wiktionary, CC BY-SA 4.0.