Sitch's Dad: He Got Fired Over a BJ at Work

The Situation's dad is hitting his son way below the belt -- releasing a SECOND video clip, claiming the MTV star was fired from a job for receiving oral sex from a 40-year-old co-worker ... inside his office.

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Frank Sorrentino doesn't offer any proof to support the allegation.

Calls to the Situation regarding the video weren't returned.