Good Grief!

From tmz, Get ready to hear Charlie Brown curse like a sailor, and wish death on a judge -- the former voice of the cartoon character went absolutely NUTS during a San Diego court hearing.

Peter Robbins was going to be sentenced for probation violations on Friday -- but suddenly went off on the judge, the prosecutor, and his public defender.

Robbins -- who voiced Charlie Brown for several TV specials in the 60s -- was convicted in 2013 for threatening an ex-gf and her plastic surgeon ... but in court he demanded a new trial, and simply lost it on his ex.

He screamed, ironically ... "She has to believe that I would kill her. I wouldn't kill her! I have never had any violent behavior!!" Robbins also barked at the judge, "Good luck to you! I hope you drop dead of a heart attack."

Not shockingly, the judge ordered a mental exam for Robbins. Prosecutors say he violated probation by drinking booze, and cutting off his ankle monitor.