Scarlett Johansson — having mastered the undercover look — hit a hot club. The normally designer-clad star of “Hitchcock” hung out at Electric Room on Wednesday incognito — in glasses and a T-shirt, and with her hair pulled back into a ponytail and barely-there makeup. “I didn’t even recognize her,” said one fellow partier after a friend pointed out the star. Johansson hung out with Sam Rockwell, who arrived after feting his newest movie at an earlier screening. Later Johansson — who was out without her ad-exec boyfriend, Nate Naylor — was spotted spending time with Lindsay Lohan’s pal, artist Domingo Zapata. “Scarlett looked like she was completely flirting with Domingo,” says a spy.