Rihanna 'Unfollows' Chris Brown on Twitter -- You Finally Crossed the Line

It seems Rihanna has finally had enough of Chris Brown ... the singer has "unfollowed" her ex-boyfriend on Twitter after he released a new diss track that appears to be aimed at her.

The song in question is a remix of Kanye's TheraFlu -- in which Brown freestyles the verse, "Don't f*ck with my old bitches ... like a bad fur ... every industry n*gga done had her."

He continues, "Trick or treat like a pumpkin ... just to smash her."

Hours after Brown released the track last night, Rihanna stopped following Brown on Twitter -- a HUGE move -- and one that's leading many to assume Rihanna believes the verse is about her.

A short time later, Brown unfollowed Rihanna.

We reached out to Rihanna's rep -- so far, no comment.