get a room
(idiomatic, informal, sometimes humorous) Used to instruct a couple to stop displaying romantic or physical affection in public.
[T]he nutcase Left and the nutcase Right are alike in virtually every particular. They should get a room somewhere -- far from here. Jay Nordlinger
I have to tell you, I'm not like Demi Moore, where the tears trickle prettily down my cheeks. My whole face screws up and it's like, 'Oh please, get a room.' Jennifer Tilly
Do they always flirt with biblical quotes?" Asil asked Tad. In long-suffering tones, Tad said, "They can flirt with the periodic table or a restaurant menu. We've learned to live with it. Get a room you guys." Patricia Briggs