I know of several who have done this. I might even personally LIKE them individually. It was, however, never "considered pretty cool" even by the wearers. I know some of the really cool fuckers on here...none of them has a username shirt that I have seen.
I was able to AVOID some of the clear...
Of course you should be allowed to have your Internet name on your football shirt.
It makes you more attractive to women and suggests to chaps that you are edgy and a bit tasty.