I want the "illiteracy" name say I'm an
English illiteracy in other words
Maybe I'm lack English skills to accurate express and understand, but some people say:
Personally, as an English speaker, I find that username actually quite amusing. I'd keep it if I were you! And no, it's absolutely not offensive or impolite. The only complaint I could see being raised is that you're calling someone else "illiterate", but as a username, this is ridiculous; usernames almost always reflect oneself, so it's a self-deprecatingly humorous username.