Undergraduates, take note:
If we have academic business to discuss -- a paper conference, say -- I will go out of my way and be up on campus for you on a day I'm normally not here. I don't have to be, and I don't expect that other faculty members ought to do the same -- this is my choice, after all. But because I have made that choice, I abjure any right to resent you for taking me up on the offer, or to loudly trumpet the sacrifices I'm making. If I voluntarily make an offer, I should follow through with a cheerful mein.
If you fail to make that appointment, even once, with no notice, just leaving me cooling my heels in my office when I could be elsewhere, you may expect that I will never again go out of my way for you. I will continue to be as helpful to you as you need me to be, but that help will come only during my regular office hours. Period.