Doesn't always work.
The late Iain McKintosh was an expert at dealing with noisy members of the audience - usually by getting quieter and quieter till other audience members told them to shut up, At one gig, a girl with too much to drink was laying forth and he made some appropriate comment which did shut her up. During the interval he saw her at the bar and apologised for embarrassing her when he was on the stage. "Oh," she said, "were you on the stage?"
Cyril Tawney was doing a gig at Stirling Folk Club when he was disconcerted by the heaving bosom of a young lady in the front row and forgot his words. "Sorry but there's this girl up the front and every time she laughs her tits bounce up and down!" She looked straight at him and said "So do yours!"

Ones that have worked - on return of a toilet visitor, "Could you hear us in there 'cause we could hear you!".
On return of another toilet visitor who made a great point of crouching while getting back to his seat in the front row. "Hey, you're supposed to tuck it in before you zip up!"

Eddie