I will tell you what irritates me the most about foot faults (from an official's point of view).
It really bothers me when I am officiating at a juniors tournament or at a collegiate match/tournament, and I call a foot fault on a player, and their coach/parents get mad at me for calling a foot fault.
A bit of background, when I am in the chair, and am there for the entire match, I will call foot faults officially from the first one I see. If I am roving, and I get called onto the court because a player says their opponent is foot faulting, I will call the first one that I see. When I am roving, and I walk onto a court on my own, and I see one that is not terribly blatant, I will let the player know on the next changeover that he needs to watch out for his footfaults, because if nobody is complaining, I don't think that it's great just to walk on court (sometimes without knowing the flow of the match), and just get involved by calling them immediately, unless it is very blatant. I will then stay for a couple of games and watch. If it continues, I will call them.
But going back to my original post, it bothers me when the parents/coaches get mad at the officials for correctly calling a foot fault, instead of getting irritated with their player and helping them correct the problem.