For me I would say it is less about humiliation than transformation. I think I've written before about how one of the sexiest moments in a scenario, especially one with a woman inexperienced in WAM, is when there is that shift from "gah! How awful that I'm enduring such a mess," to, "yeah! How awesome that this is so sensual and fun." That first smile from a well-dressed woman caught in a rain storm, that first bit of laughter from a human sundae in progress -- nothing moves me quite like sharing in those moments. Seeing them captured or even staged in media can also be inspiring.
However, a big factor for me is attire. If a girl shows up in lingerie or a bikini, then that transformation cannot be as dramatic as it would be if the scenario begins with her fully clothed in something elegant yet still flattering. A woman in nice office clothes diving into the mud can really hit my sweet spot, whereas a girl in modern swimwear doing the same thing will have much less of an impact on my state of mind. I suppose this is psychologically very similar to humiliation, though if a girl was deeply distressed or truly saddened by an ordeal, that would rob it of all appeal to me. Perhaps the most dramatic example is this -- watching a scene in a horror movie where a terrified character is being drenched in the blood of her friends has zero erotic value to me, but meeting up off camera with an actress covered in fake blood likely would excite me.
Also, visual contrast is important to me. On the simplest level, this means situations like white cream on a white blouse or ketchup on a red dress have diminished effect. Fetish wear like PVC or latex clothing, if tasteful and well-fitted, can look enticing to my eye. Yet when it comes to sploshing I much prefer playmates wearing fabrics that change appearance when wet or stained. Even though modern cleaning techniques can save most clothes from most ordeals involving food or mud, if a nice dress or blouse and skirt ensemble appears to have been hopelessly trashed during play, so much the better to me. Likewise, it matters to me if women involved have clearly put effort into their look beyond the outfit. Meticulous hair and makeup, along with a few nice accessories, really adds something to it for me. Ultimately what I like to see or join in is a transformation from immaculate conventional beauty to utterly sloppy mess.
Yet oddly enough, I prefer not to dress formally for my own involvement in such play. Ideally I start out in a simple jersey and jeans while my playmate is much more stylishly dressed. That said, a time or two I've begun nude on request (not counting shower sex, which to me doesn't even seem like WAM unless someone enters the shower fully clothed.) Also, I can still enjoy wrecking a woman's casual clothes if they are not too bulky (I'm not a sweater or coat guy,) too skimpy (short skirts look great to me, but minimal tops or short pants do not,) or downright unflattering (my ideal date or model often has the wiles enough to look fine even in a simple denim outfit, and my mudlarking experiences typically occur in the context of hiking or camping trips, but some have trouble bringing their inner sex goddess to the surface without dressing up for the occasion.)
In terms of the woman herself, there really isn't any difference between the sort I would date in a conventional way and those I would introduce to this kink. It is such a complex judgement that there is no way to set up ironclad criteria. For example, short hair is often a dealbreaker for me, but every once in a while someone catches my eye as truly gorgeous in spite of having something like a pixie cut. Likewise, I'm not a fan of breasts a great deal larger than average, yet the one true love of my life is well-endowed in that area. I guess ultimately it is a holistic assessment that determines what works or does not work for me.
As far as the other questions go, bondage has an interesting role to play here. In terms of real interaction, I do not like to leave a woman restrained for long. Not only are there risks involved (loss of circulation for any substantial length of time can produce serious injuries,) but also I prefer playmates able to involve themselves actively in our fun. Give and take does more for me than unilateral domination. That said, the sight of a well-dressed woman in restraints is sure to catch my eye. Bondage play can give me a little rush of power, but more importantly it can send a submissive playmate into a uniquely wonderful altered state, provided a strong voice of authority is brought to bear on her situation. In terms of erotica, bondage never turns me off; but in terms of actual play, I prefer to use it only when it presses my partner's proverbial buttons, and even then just long enough to put her mind into "subspace."
I never really chimed in on the "what is WAM?" thread because I agreed with where it stood. It is hard to justify narrowing the definition in any way, since any changes I could devise would have excluded legitimate elements of the phenomenon. I know for me a woman getting slimed in a satin blouse and leather skirt does something special that a woman getting slimed in a bikini generally does not, but I am not so self-absorbed and arrogant as to argue that a reversal of such personal polarities invalidates involvement in WAM.
Perhaps in time thinkers will subdivide this interest and/or mesh it with clinical psychology. For now though it seems somewhat a mystery. For example, clearly some manifestations of WAM do overlap with salirophilia, and I know I see the appeal of ruining an immaculate look, but deliberately spitting on a girl is both unsexy and distasteful to me. On a behavioral/mechanical level, what we have here is an underinvestigated psychosexual anomaly. We may have much yet to learn about this particular quirk, but fortunately we do not need to know every little neurochemical nuance of it to experience heights of pleasure the likes of which many people lack the opportunity to attain at all.
Regards,
messydom
Though I will say I never get tired of the brat routine or setup; it is always hot when the woman, if you will, deserves the pie. I also prefer not too much to get in the hair. And excessive mess doesn't do it for me; clean-faced hits are where its at.
. i also like the feeling of someone else being in control and having their way with u. one thing that really sets me off though is when i kinda get in the mood to do something sexual with my partner, i like to cover her face(or she cover mine) and not wipe off the mess and go to work on them or me lol 
