Cute! The wonky top stitching just add charm. I've been meaning to make a few of these for awhile, but it never seems to make it to the top of my list. Does yours have a closure at all (like velcro) or is it just a full circle?
They provided the materials at Sew Po and used this pattern: http://cosmocricket.typepad.com/cosmo_cricket/2011/12/coffee-cup-cozies-free-pattern.html
I used another style before that I actually like better with an elastic/button closer that. I can't find the pattern now, but it's like this: http://craftystaci.com/2011/01/10/reversible-coffee-cup-sleeves/