The Situation -- No Gel, No Abs, No Alcohol

It was a totally different Situation in Las Vegas last night ... where the "Jersey Shore" star celebrated his birthday without any of trademarks making an appearance.

Sitch turned 30 back on July 4 and finally got around to celebrating in Sin City at Señor Frogs, located inside the Treasure Island hotel. The night was very low key -- not only did Sitch not gel up his air or flaunt his abs ... but our spies say he didn't touch a drop of alcohol.

Change is good.