Yes, I think there are some things we compromise on (it's not hard to have a certain color of cup/plate, and helps them with a bit of a routine, etc. PS: I love you Ikea, for your 6 packs of kids dishes!) and some we don't (you may not WANT to share, but you will learn).
I don't know, I think the only thing to do is consistently reinforce what you expect of him. At 20 mos, he understands you even if he can't vocalize himself yet.
I would be making him wait until he is calm and quiet to get his snack, etc as well. Cry and scream all you want, it doesn't make it come to you any faster!