A slingshot; hence n beany crotch a forked stick for making a slingshot; a slingshot.
1920 Illustr. World 33.317, Do you remember, in the good old barefoot days, when you would make a sling-shot or bean-shooter—sometimes called “beanie”—of a crotch from a tree branch, a strong rubber band, a piece of leather and some string? 1938 Chester Times (PA) 7 July 9/6, [Syndicated story:] Tommy pulled his beany crotch out of his hip pocket and fitted a small ball bearing into the sling. 1949 PADS 11.17 CO, Beaney. . . A small sling-shot. 1950 WELS (Weapon used by children) 1 Inf, swWI, Slingshot, beany. 1963 Burroughs Head-First 107 CO, From time to time I have mentioned a “beany,” a piece of equipment that no boy of my generation in his right mind ever ventured abroad without. Succinctly, a beany consisted of a willow crotch in the shape of a V with a handle on it. 1971 New Mexican (Santa Fe NM) 14 Feb sec D 7/4, We didn’t aim our rubber-powered weapons at men, although some kids of southern lineage had a name for them that implied such use. Instead, we called our gadgets “beanies”—which implied enough. 1987 in 2015 DARE File—Internet AZ (as of 1920s), We would climb up, climb the hill. We’d look for beanie-crotches? [DARE Ed: transcriber’s query] and hunt for squirrels or whatever we could, you know, in those days, with slingshots. 2014 Ibid csCO, We made our own bean-flippers from a forked stick and a piece of rubber from an old intertube [sic], and a piece of leather for a pouch which held the rock. Our beanies were for shooting birds.