Green’s Dictionary of Slang

1. a dislikeable, unsuccessful person.

1993

Eble Campus Sl. Oct. 5: stain – loser; a mean-spirited person.

2. a drunk.

1994

Eble Campus Sl. Apr. 8: stain – drunkard.

3. (UK black/gang) a victim.

2018

Digga D ‘Mad About Bars’ 🎵 Really tryna bullet that boy [...] / I look psychotic when man get wassy / I need me a stain.