The issue is this: one PC has a paladin -- he is normally a very happy, shiny person who loves everyone and whose hair shines and whose teeth glint in the sun. He's basically The Tick in plate mail. There was a situation last game in which the PC thought that the Tick might lose his temper (a very rare thing, but understandable given the extreme circumstances), and the PC wanted to know what she should roll to see whether or not that happens.
Put on the spot, I told her that the Tick's logical mind was trying to overrule his emotions, so to roll INT (plus half level) vs. Will; if she "hit," then the Tick's logical mind won out, and he kept a lid on his temper. Not bad for a spur-of-the-moment call, I don't think, but in hindsight I don't like it.
The higher a character's Will defense, the better they should be at keeping their temper in check, no? So the "attacking" value should be representative of the character's anger, rather than the other way around. But what value to use? I like the idea of using the Will defence against temper (or temptation, because I can see this kind of thing popping up for other characters), but what to use in opposition to it? Should I just ask the player "How difficult do you think this test is for your character?" and use their answer to determine what attack value to use?
How would you have handled it?