Hmm, I think a few things about that were rude - hogging all of the prawns is pretty rude, confronting someone is pretty rude, but talking about other people is a bit rude too.
TBH, my expectations of people in all you can eat places is pretty low - it seems to bring out the mentality of "I'm just going to take far more than I (or a small african nation) could ever need to eat, just because I can" and I think that is quite gross! Off topic, I also hate those place that do the 'challenge' steak "Can you eat half a cow just to prove you can?". So wasteful and like 'all you can eat', brings out the worst in some people! Vent over!