Billy Joel acted like a regular Joe in Midtown this week until a pal reminded him he was a VIP who couldn’t just mix with the masses.

Spies at the opening night of Sting’s Broadway musical, “The Last Ship,” at the Neil Simon Theatre said that after seeing the show along with Bruce Springsteen and Paul Simon, the “Piano Man” singer was “standing in the middle of the street outside.”

But a friend called out to him, “What are you, crazy? You can’t go out in public!”

Joel was then escorted to his car by a cop to keep any potential frenzied fans at bay.

Perhaps he felt comfortable on the block because the show plays on 52nd Street — the name of his 1978 album that includes hits “My Life,” “Big Shot” and “Honesty.”