'Bad Girls Club' -- Redd Fails Drug Test ... Gets Locked Up

Alyssa "Redd" Carswell can't get back to the "Bad Girls Club" mansion fast enough -- the ex-reality TV star just got busted for failing a drug test.

Cops in Tallahassee, FL tell us she turned herself in Friday night after she learned there were warrants out for her arrest. Carswell is on probation for a 2012 stolen property case, and has to submit to regular drug testing -- but last month's test came up dirty. Hence the warrants.

Redd tells TMZ, she failed because she was smoking pot -- which she admitted to cops.

She's hardly keeping her nose clean -- you'll recall, last summer co-star Natalie Nunn filed a battery report against Redd ... accusing her of chomping down on her foot during a fight. The L.A. City Attorney rejected that case for lack of evidence.

Once a bad girl, always a bad girl.