> A common joke in the mathematical community is to say that "trivial" is synonymous with "proved" — that is, any theorem can be considered "trivial" once it is known to be true. Another joke concerns two mathematicians who are discussing a theorem; the first mathematician says that the theorem is "trivial". In response to the other's request for an explanation, he then proceeds with twenty minutes of exposition. At the end of the explanation, the second mathematician agrees that the theorem is trivial. These jokes point out the subjectivity of judgments about triviality.
from http://en.wikipedia.org/wiki/Triviality_(mathematics)
Trivial doesn't mean easy. Just that it has been shown before or that new information won't be derived in the proof.
If you know how well the person you are talking to know the material you are talking about, then I don't find calling the thing 'easy' is humiliating at all, instead it is a effective way to say "no worries, just do XXX and you are good". A rule of thumb is when you are not sure if it is appropriate to call something easy, just ask the person you are talking to whether he knows that thing. Why stopping using the word 'easy' when we are sure all parties of the conversation gets what you are talking about and think it is indeed easy?