I guess it depends on how well you know each other. I often have people walk in, and walk right up to me and call up a tune .... knowing that they are a "regular" in the room and they are welcome because I've made them feel that way in the past. I even have friends that my audience requests to hear because they know what to expect !
Donny is one of them ..... he's getting to know all my Friday night people, and they ask for HIM to sing too ! It's a very friendly place ........ like "Cheers", only I'm Sammy's boss !