As a guy who considers myself on the lower end of "average" when it comes to my appearance, I was wondering how big a factor a guy's appearance is in deciding whether or not you want to trash him (or let him trash you) - or even in how you want to trash him (or have him trash you).
(I realize I wrote that from my own preferred m/m perspective, but folks into other gunge dynamics are also welcome to respond.)
I think shape and size is largely irrelevant once someone is covered in slop... mainly due to the fact they're normally unrecognisable.
If a guy has a cute face, nice hair and good features to mess up then yes that's probably a bonus but it takes all sorts.
My fetish lies in messing up a guy with decent / thick hair... the longer the better.
So I think you'll get a mixed bag of answers... and probably some fickle ones. But gunge is just like dating... and life... everyone will have varied opinions and there will be some thet are fickle too - and to me, they don't matter!
Personal opinion: not very. Compatibility in scenes, energy, personality, reliability, and availability are several traits I would rate much higher than body type/physical appearance.