I’m running a character that uses a non-PHB class, to wit the wu jen from Complete Arcane. One of the things about this class is that, every ~3 levels, you have to pick a “taboo”, something your character isn’t allowed to do lest she lose her spellcasting ability for a day.
My problem with this is that most of the example taboos are things that you don’t, in D&D, really have to deal with. “Oh, by the way, I never cut my hair,” you say, and voìla! your taboo for that level is fulfilled. Even stuff like “make a small sacrifice once a day” doesn’t specify that you actually have to spend any money on it–heck, you could say that you prick your finger every day before memorizing spells, and that’d cover it.
So for Altariel’s 3rd-level taboo, I picked one I’m actually going to have to roleplay: Cannot lie. (Note that this is in the sense of “cannot make an untrue statement”, rather than “cannot allow someone to come to the wrong conclusion based on what I say”, but still, it makes perfect sense.) If the universe is to be expected to listen to me when I say there’s a fireball over there, I can’t go around telling lies about other things, now can I?