I couldn't even spell accessorizing, if that is any indication of how infrequently I utilize such a thing. But I'll tell you what I do do. I choose a mug that matches my outfit. Most of the mugs at the office are black or green Ikea mugs. There are a few exceptions, and I have one most favorite mug. It is a really nice color and shape, and it has a cute little handle. But it is a specialty mug. I'm always a little hesitant to take the specialty mugs, because they might be someone's own personal mug (although that didn't stop me from once using the mug that has a person's name on it.. desperate times require coffee, one way or another).
Anyhow, I don't use my favorite mug often, but when I do use it, I make sure it will match my outfit.
Makes for a pretty good accessory, wouldn't you agree?