I can think of nothing the French love to do more than cut in line. Anytime there is a queue, the French feel obliged to walk immediately to the front and pretend as though they are oblivious to the crime they have committed. When I was still new to France, I used to just let it go and not say anything. Not because I didn’t want to, but because my argument would have no impact as I did not speak any French. Then as I progressed, I started a new tactic. Anytime someone would cut I’d say, “WHAT THE F#%K!!” which seemed to be a little startling. Even if the perpetrator did not speak English, they knew what you were saying.
Alas, I have discovered an even more perfect line of defense against this blatant disregard for social norms. It involves fighting back with another social taboo. The next time someone cuts in front of you. Start a coughing fit. The kicker, do NOT cover your mouth. Cough all over them, and in their general direction!! How gross is that? The beauty is they cannot do anything about it without indicting themselves. So they, a) have to take it and miserably regret they ever cut you, b) say something to you thereby acknowledging their fault, at which point you can rightfully call them on it, or c) they leave the line (nobody wants what you pretend to have).