Thompson's frustrations boiled over on September 25 during a routine meeting at Corrections' Stuart St offices.
After he said his nephew had moved into his home, he was directed to sign a letter acknowledging he was barred from contact with under-16s.
Thompson began speaking loudly then threatened to overturn the table at which they were sitting.
"I'm going to smack you in the face," he told the victim.
"The defendant stood up and with his fists clenched stated: 'I will pin you against the wall and smash your face in'," a police summary stated.
As the Probation officer left the room, Thompson told him: "ex-prison officers deserve everything they get".
Concerns about the defendant's behaviour led to a warrant being executed, which uncovered a secret cellphone. Thompson had been using it for four weeks since the start of September, the court heard.
He had failed to inform Corrections of the phone's existence, therefore breaching one of his obligations.
Thompson later pleaded guilty to that, along with a breach of release conditions and threatening to commit grievous bodily harm.
Judge Michael Turner sentenced him to six months' imprisonment.
Thompson is one of 2399 child sex offenders in the country registered since legislation was introduced in 2016.
Corrections data (from September last year) showed 1290 of those offenders were incarcerated.
Earlier statistics placed more than 100 of the country's total (both in prison and out) in the Southern region.
