The "Stefan walk" involves flailing one's limbs around in the manner of someone who is either in pain or of invalid mindset. They usually withhold at primate stance whilst chanting jibberish and saying things that no one but them find funny.
It really is quite a sad site to observe.
Stefan: HARRY PORKER AND THE PHILOSOPHER'S BONE
All: Well that's gay...
Stefan: Nono, it's not, abbbueuue hehehehe...
*initiate Stefan walk*
All: *Facepalm* He's doing the Stefan walk again, what a dunce.