In English, relative formality is less a question of grammar than of vocabulary and syntax, whereas other languages -- Spanish, for example -- use a different set of verb conjugations. In an informal situation, I might say, "Gimme that." But the formal expression would be "Would you please pass me that?" More idiom than rule here.

Why is this important? Language expresses the vast range of human relationships, and some are more formal than others. If my brother and I are watching TV and I say "Would you please pass me the chips?", he would assume I was joking or angry at him or had been replaced by a robot. But if I were having dinner with the President and said, "Gimme the potatoes," I might be thrown out before the dessert arrives.