I would like to say "Will you shut that f*cking thing up-this song doesn't have a beat-I'm not giving it one, so why that F* ck are you ?".
In reality , I would look at the person , grim-faced with pressed lips and move my head in a manner which say No-No - not required. Most of them who do this sort of thing are well meaning and enthusiastic and I would think new comers , so it's difficult to be hard on them, however, there's a time to be cruel to be kind in educating them that some things simply don't mix as for instance playing that thing with the beads when someone is singing Wild Mountain Thyme.
Watch some awkward B*stard write in and say it would work for them !!!