Playboy Babe Liz Dickson -- Ass Cheek Golf Swing VIDEO ... You Gotta See This Bruise

No wonder this chick's so teed off -- TMZ has obtained video of model Liz Dickson taking that golf club to her ass at a Playboy event ... and it's gnarly as hell.

TMZ broke the story ... Dickson is suing Playboy for more than $500,000, claiming she was badly injured at a Playboy golf tournament in L.A. back in 2012 -- after she was asked to lie on her stomach with a tee between her butt cheeks ... while comedian Kevin Klein took a golf swing.

The video is crazy -- but the photo tells the real story.

In addition to the massive welt, Liz Dickson's attorney tells us, the model damaged her hip ligaments and nerves as a result of the accident. He also says she's incurred more than $33,000 in medical bills so far ... and still feels numbness and tingling in her right leg.