We really are splitting hairs here people.
Anyway Delta, it's not exactly improper to think about the term Falmer negatively when a snow elf is in front of you, they are one of the same, and faire looks nothing like those beasts that everyone associates with the term falmer. 
As a matter of fact Falmer may not actually be the elvish term for Snow elf, but for the creatures that used to be snow elves. For instance, it being translated to the Fallen elves. You know the snow elves being the epoch of Skyrims civilisation until the nords came along and put an end to that, and the dwemer putting the nail in the head.

So the saying "Fall from grace" applies very well here.

Not sure of this is correct but never the less it's applicable that the term Falmer may insult a snow elf.