Tom Izzo's won the NCAA tournament and been to 7 Final Fours ... but from the looks of it, the happiest moment of his life was being on the set of "Judge Mathis."
The legendary Michigan State basketball coach was a special guest on the courtroom reality show ... and dude was cheesin' like it was his damn wedding day.
Mathis was presiding over a diehard Ohio State fan (from Michigan!!), so he had to throw shade and shout out Coach Izzo -- who couldn't get enough.
Fun fact: Judge M says his daughter was a student assistant for Izzo ... so it's no surprise that they bro'd out backstage during the taping.
Mathis even dropped the gavel on rival Michigan coach Jim Harbaugh, captioning their pic: "I hear you are a Judge Judy fan. Izzo wins!"