Chad Johnson is going to jail.

And, it's because of a playful slap on the rear end of his attorney while in the courtroom.

The former Chad Ochocinco was appearing in court on a probation violation after his domestic violence charge involving ex-wife Evelyn Lozada.  There was a plea deal in place for no jail time, but the judge in the case rejected it after the slap, saying Johnson wasn't taking things seriously enough.

Judge Kathleen McHugh extended Johnson's probation by three months and sentenced him to 30 days in jail.