Green’s Dictionary of Slang

beany adj.2

[off one’s bean under bean n.1 ]

1. (US) eccentric.

[US]J.C. Ruppenthal ‘A Word-List From Kansas’ in DN IV:ii 103: beany, adj. Mentally defective, whether feeble-minded or insane.

2. lively, spirited, usu. of a horse.

[Ind]‘Sir Ali Baba’ 21 Days in India 112: We have been out since early morning on the jumpiest and beaniest of Waler mares. I am not killed, but a good deal shaken.