They've been around for a couple of days now.
They're just websites that play a soundclip over and over again with a message and a picture in the background. They can be very funny if done right.
The original one that started it all, for people with no idea what a ytmnd website is:
www.yourethemannowdog.com
Well as of the past few days, ytmnd.com has been hosting these user done websites. All you need to create your own is a soundclip and a picture. You can register an account at ytmnd.com and create your own.
These are a couple of good ones that I've seen:
http://becauseyoutouchyourself.ytmnd.com
http://mahspoon.ytmnd.com
http://stapler.ytmnd.com
http://tatatodayjunior.ytmnd.com
Everyone's favorite: http://picard.ytmnd.com
and my personal favorite:
http://fevercowbell.ytmnd.com
Yeah, they're pretty funny. I've been dying to see a "tonight I dine on turtle soup" one but I don't know how to make them.