EXCLUSIVE

Justin Bieber bought himself a penis enlargement with a stolen credit card ... and he's also cheating on his GF with Ke$ha, Rihanna 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.

Among the highlights:

-- "Bieber has cost me $426.78 and never paid me back. This money was used as abortion money because Justin Bieber got my daughter Selena pregnant in my bedroom, on my canadian bear rug."

-- "Usher Raymond came to my house on the forth of july 2012 and sodomized me with a firework and lit it inside my anal area while blaring kate perry [sic] firework song in my ear drums."

-- "[Bieber] gave selena a std and Bieber stole my credit card to buy him and sean p-ditty [sic] combs cocaine to use in drug free school zones."

-- "Bieber also got a penis enlargement with my stolen american express card. "

The lawsuit concludes ... "I'm an emotional mess ... America must boycott biebers music!"