JOJO PLEADS GUILTY & GETS A SLAP ON THE WRIST!

Joseph Simmons, Jr. -- son of rap legend Rev Run -- just pled guilty to one charge of disorderly conduct in New York after being busted last May for marijuana possession.

As part of the plea, the 19-year-old's possession charge was dropped -- he'll only have to serve one day of community service. That's gotta hurt.