Alcohol reduces inhibitions and loosens tongues ( Fecundi Calices,Quem Non Fecere Disertum ?)---So,it isn't a problem that is ever going to go away ! It will always be particularly annoying in a venue where the bar is integral ; last year at Towersey,the concert with Paul Jones et al,was ruined (for me,anyway) by the rising tide of raucous laughter,ribaldry,guffawing,shouting and general bonhomie emanating from the ever-increasing throng ( I won't say rabble !) at the back of the marquee ....in fact,by the interval,they occupied virtually half the available space !
    I reckon the best bet is to A) employ mute bar-staff,and B) for an "MC" or other designated person to get up every 10 minutes or so and shout "OK-- Dirty Joke / Piss / Refill Break ! ".