If you've ever been accidentally stabbed with a knife or whatever, you can double or tripple that pain. That's why I said stabbed with a sword. While I haven't had exactly that happen to me, I have had worse so I can very much imagine that's what it would feel like.
Yeah cleanup can be a slight pain too though, but don't say you'd do anything to avoid messing yourself. If it came down to pooping diaper or real physical harm I'm sure using your diaper would be the lesser choice of two evils.
Truth be told too, if you can get past the cleanup and smell then messing a diaper can actually be stimulating and fun, even sexually stimulating. It's why some people actually like it so much. Heck, I myself have sometimes "taken advantage of a bad situation". I figure if I'm already messy, why not get in a little play time while I'm at it?