Washington Wizards player Kelly Oubre, Jr. ain't throwin' any punches, but he's still going for a knockout ... getting a custom-made, 14k white gold grill with his "K.O." initials on it!!

TMZ Sports has learned ... KOJ decided to treat himself to the white and purple VS+ diamond piece ... and hit up jeweler IF & Co. about a month ago for the job.

We're told Oubre dropped $12,000 for the finished product ... which is pretty tame compared to what other athletes have paid for their blinged-out mouth pieces in the past.

Regardless, the grill looks fresh as hell.