Tyga -- Blac Chyna's Just Bitter She Can't Have Me!

Tyga is sure Blac Chyna's custody play has nothing to do with parenting and everything to do with the fact he is with Kylie Jenner, and not her.

Sources close to Tyga tell TMZ, he doesn't think his relationship with Kylie is any reflection on his ability to be a good dad ... and no one -- not even BC -- can legitimately question his parenting skills.

We're told Tyga believes any attempt to wrestle custody away from him is simply because he chose KJ over BC.

Our sources say Tyga thinks if anyone is questionable it's Blac Chyna, whom he claims cares more about twerking than raising their son.

The couple does not have a formal custody arrangement, but it seems they are headed for an all-out custody war.