Chris Brown -- My Baby Mama's Got Terrible Judgment In Boyfriends

Chris Brown is chomping at the bit to face his baby mama in custody court ... and the biggest weapon in his arsenal is the woman's boyfriend.

Chris and Nia Guzman will fight it out in 2 weeks. She wants full custody of 1-year-old Royalty and visitation for Chris, BUT only if it's monitored. She says he's a bad guy who hangs with criminals and smokes weed. Chris wants joint custody.

But we're told Chris thinks her argument will boomerang right back in her face, because her boyfriend, King Ba -- the guy who lived with her and is even named on Royalty's birth certificate -- is a wanted man ... on the run for felony forgery.

We're told Chris is eager to tell the judge Nia has terrible judgment ... hooking up with a con man.

As we first reported, Chris believes Nia's real motivation has nothing to do with custody ... she wants to squeeze more child support out of him. He's currently paying $2,500. She wants $15k.

As for Nia, her rep tells us, she's no longer with King Ba.