Justin Bieber bought himself a penis enlargement with a stolen credit card ... and he's also cheating on his GF with Ke$haRihanna and Penelope Cruz ... this according to a CRAZY new lawsuit filed in court and obtained by TMZ. 

Bieber has been sued in Michigan by a man claiming to be Selena Gomez's father -- who makes some of the most insane, and obviously untrue allegations ever documented in court. 


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