I really love the way user flair works, but unfortunately it doesn't look very sharp on a Retina display, especially when juxtaposed with browser-rendered text. If you made the generated image twice its current size, it would circumvent this problem.
Could you please generate larger source images? Keeping the same width and height HTML attributes will mean that the image won't look any different for current users, so there's no chance of anything breaking.
It's a small difference, but quality is in the details!