I spent a summer reading everything Wikipedia had to offer about sexual fetishes. Interesting stuff.
Since then, I've been able to pepper everyday conversation with vocab like hybristophilia (hot for criminals) and ABDL (adult baby diaper lover), as well as confidently make assertions like "Stacey London from What Not To Wear has a following among nostril fetishists." In short, it has enriched my life and the life of those around me.
Being an expert in this area has made me highly attuned to deviations from the norm. I can smell a fetishist from a mile away. I suspect some of my closest friends and neighbors are fetishists. I can tell when someone is a fetishist before they even know they are.
So anyone in my position would freak out when they saw the Yea Yeah video for the first time. Wet and messy, anyone?
A wet and messy fetish (WAM) is a form of sexual fetishism whereby a person becomes aroused when substances are deliberately and generously applied to the naked skin, or to the clothes people are wearing. 
Messy substances can include whipped cream, mud, shaving foam, custard, baked beans, pudding, chocolate sauce, peanut butter, Japanese-style lotion, paint, oil or gunge/slime, etc. A subject will often be pelted with cream pies or sit on cakes. Wet substances are mainly water but can also include other liquids such as fruit juice, milk or alcohol (usually beer).
Matt and Kim are obviously giant pervs. Onward.
The second video, for Daylight, is a little more difficult. At one point, they do get garbage dumped over them, and Matt gets water in the head, so WAM.
But they also spend the whole thing crammed into small spaces. A combination of crushing and total enclosure that we can call claustrophilia. Even if I cannot find an entry in Wikipedia, someone is into that shit. And I'm guessing it's Kim.
The latest video renewed my sense of purpose.
Lessons Learned is a straightforward exhibit of exhibitionism.
Exhibitionism, known variously as flashing, apodysophilia and Lady Godiva syndrome, is the psychological need and pattern of behavior involving the exposure of parts of the body to another person with a tendency toward an extravagant, usually at least partially sexually inspired behavior to attract the attention of another in an open display of bare "private parts" — i.e., parts of the human body which would otherwise be left covered under clothing in nearly all other cultural circumstances. Some researchers have claimed that telephone scatalogia is a variant of exhibitionism.
So Matt and Kim, a couple in band and IRL, are fetishing all over us, their public. Imagine the hijinks they get up to behind closed doors! Or, maybe they are laying on this fetish business in an attempt to drum up some sexual interest in the band. It's cool though, because Matt is staggeringly handsome.
Remember, fetishizing is not a crime at low levels. It becomes a paraphilia when it interferes in your life. Matt and Kim, by all accounts, are healthy, functioning adults who provide entertainment to millions.
In closing, each video is a paean to a different fetish. It's a cool strategy because they will never run out of ideas. Unless they are unaware of what's going on, then that is troubling and they are in for a brain shakedown shortly. (Someone will come home and find someone tied up...) Anyway, I can't wait to see what they do next!
Also, on a side note, is the future of music videos band porn?