Rihanna -- Goes Hardcore with New Tupac Thug Life Tattoo

Rihanna must be a huge Tupac fan ... because she just tatted the words THUG LIFE -- on her fists!

RiRi hit up an LA tattoo parlor yesterday to get her hardcore ink started ... it doesn't look complete in the photo she tweeted out early this morning. It could be a temporary tat, but still ... badass.

Interestingly, the t-shirt she was wearing while she got inked up -- John Lennon's face. Totally thug.

Rihanna also ran into Danny Trejo at the tattoo parlor. Hope she's not inspired by his massive piece of chest art.