Lampshaded (hilariously) in The Last Hero.
Rincewind: I do not wish to volunteer for this mission.
Lord Vetinari: I beg your pardon?
Rincewind: I do not wish to volunteer, sir.
Lord Vetinari: No one was asking you to.
Rincewind: (wagging a weary finger) Oh, but they will, sir. They will. Someone will say: hey, that Rincewind fella, he's the adventurous sort, he knows the Horde, Cohen seems to like him, he knows all there is to know about cruel and unusual geography, he'd be just the job for something like this. (sighing) And then I'll run away, and probably hide in a crate somewhere that'll be loaded on to the flying machine in any case.
Lord Vetinari: Will you?
Rincewind: Probably, sir. Or there'll be a whole string of accidents that end up causing the same thing. Trust me. sir, I know how my life works. So I thought I'd better cut through the whole tedious business and come along and tell you I don't wish to volunteer.
Lord Vetinari: I think you've left out a logical step somewhere...
Rincewind: No, sir. It's very simple. I'm volunteering. I just don't wish to. But, after all, when did that ever have anything to do with anything?
- Note that very few people manage to even momentarily confuse the Patrician. Rincewind is a sort of singularity. (The Patrician seems rather off his game generally in The Last Hero; he does a couple of other things that are not quite in line with the Crazy-Prepared Magnificent Bastard we've come to know and love. The world is about to end, so he's got some excuse for being distracted.)