Jenelle Evans Arrested For Assault ... Hits Ex-Fiance's New GF With Glass

Jenelle Evans might as well have a designated cell in the local jailhouse because she was just arrested AGAIN ... this time for beaning her ex-fiance's new girlfriend with a glass.

Law enforcement tells us Evans' ex-fiance Nathan Griffith showed up at her South Carolina home to get his belongings. He brought along a new girlfriend, which didn't sit well with Jenelle. We're told Jenelle came charging out of the house and threw a glass at the girl, striking her in the head.

Cops were called and they placed Jenelle under arrest for assault.

A rep for Jenelle says the 'Teen Mom 2' star felt Nathan was provoking her by bringing over the new girl. If you're counting ... Jenelle has been arrested at least nine times.

She's still in custody.