Broadcasting 101 -- ya may not wanna call your ex-wife a "dingbat" on live TV ... 'cause everyone knows that's pretty bad, right??
But, former Chicago Cubs star Mark Gracemust've missed that lesson ... and now he's apologizing for his bizarre rant during Saturday's game.
The 56-year-old joined Len Kasper and Jim Deshaies in the booth (virtually) for the Cubs vs. Brewers game on Marquee Sports Network over the weekend ... when he was asked to give a fun story about his playing days.
That's when Grace couldn't help himself but call his ex a "dingbat" several times while sharing an incident where she accidentally parked in a spot reserved for then-Brewers owner Bud Selig ... forcing Grace to rush out in full uniform to stop the car from being towed.