One of Frank Sorrentino's business associates tells TMZ, Frank had asked Sitch for some help making his monthly medical insurance payments recently -- and the "Jersey Shore" star flat out refused.
According to sources, The Situation not only said no -- but told his dad to "move to Florida and go on welfare."
We're told Frank was pretty adamant about repaying his son anyway -- using money from a business deal they allegedly made to develop real estate in NYC ... but the Sitch never gave him a chance.
Frank was outraged by his son's rejection -- and responded by RIPPING the Sitch into pieces online yesterday in multiple angry videos.
Sitch released a statement earlier today, saying he is "extremely saddened" by his father's actions.