They sure can make you question why do you try so hard to be nice to them ... seems to take the heart and the patience of a saint to keep "killing" them with kindness.
...but make no mistake about it, altho he may be unwilling to show it right now, he does know what you did for him and he isn't likely to forget. One day he will surprise you by bringing it up, even indirectly, and thanking you for it.
Keep striving to make today better than yesterday...
