SVB I know it's not natural for an American (are u American?) to impose one's self in a restaurant, but believe me, the best way to gaining respect is NOT being embarassed or uncertain in what it is you want. Your chicken was clearly undercooked which, even for me who likes all sorts of meats "undercooked", is just not right. You're the boss in a restaurant. And by that I mean you have to show that you know what you want and, as long as it's not an outrageous demand (but even then...), you are absolutely in your right to request whatever you want. The key is confidence. If you show hesitation...uncertainty...embarassement...etc. the waitstaff will "eat you alive" and definitely take advantage of that weakness. A good metaphore for someone who lives in New York is crossing the street in NY : rule n°1 : never show fear rule n°2 : never run while crossing the street unless absolutely necessary (ie you'll become a statistic if you don't) It's all about confidence. Well, it's the same thing in a Paris bistro.
"Undercooked" is a sliding scale depending if you are in an American restaurant or a French restaurant. Chicken, porc, veal, etc should never be "bloody" (ie you shouldn't see red blood in any of those meats when brought to the table) whether you are in France or the US. However, "pink" is another matter (from what I understand that was not the case here). Therein lies all the subtlety of cooking the above-mentioned meats. They are quick to become stringy and dry if overcooked and believe me a well-cooked (ie pink) piece of porc or chicken or veal is absolutely stunning. The moist, juicy flavour when done just right is sublime. By the way, one of the reasons that a piece of chicken arrives undercooked (unfortunately this is happening more and more) is because the chicken was frozen when they started cooking it and therefore the exterior grilled well but the interior didn't have time to thaw/cook. That said, I prefer to be confronted with an undercooked chicken (which I can send back to finish the cooking) than with an overcooked chicken... So just send it back, have another glass of wine while you wait and pay no attention to a waiter's bad mood.