Green’s Dictionary of Slang

a derog. term for a Mexican.

1978		Maledicta II:1+2 (Summer/Winter) 151: Bean-eater, Beaner, Beano Any Chicano, Mexican, Latin American, or other brown-skinned person for whom beans are a dietary staple. Still a fighting insult, but less so since the movie ‘Freebie & The Bean,’ with a Chicano narcotics agent as co-hero.
1989		H. Rawson Dict. of Invective (1991) 228: bean, bean eater, beaner, and beano, all for a Latin American, usually a chicano.