Ashton Kutcher and Demi Moore could have used bathing suits the other night. The couple showed up at the Hotel Rivington for a party thrown by Foursquare, and spent the evening hanging out next to a hot tub full of half-naked girls on the hotel rooftop. “I don’t think a lot of people even realized it was them,” says a spy. “They were dressed down and Ashton was wearing a hat.”