Well there is nothing special about this act. If you won't believe me -try it yourself. To start, you need stretchy pants (yoga pants or pyjamas), put your feet in each end of pants and put one foot in front of the other. Then you push down on your legs alternately and keep doing this until they go up. Lastly, you can squat to put your pants over your butt, then tadaa....
I just tried it with my pyjamas, so if I can do it then you can do it too, just like this guy.
Try it... it may look retarded but its FUN.