In moderation for good reason, I have no problem with a few coach passengers using the FC head. When, however, a line of coach passengers forms in FC, I ring for the FA and ask that they clear the aisle to allow the FC passengers to use the restrooms first.

I am not trying to be imperious or condescending, but a quiet, relaxed, civilized atmosphere is the main reason I always do my level best to fly first class and I feel my miles, certs, whatever, have purchased that privilege.