ad-hominem, such as you're engaging in
I am? Quote me.
If his username isn't appropriate here
The question is not of "appropriateness". Choices you make provide information about you. The more idiosyncratic choices you make, the more information these choices provide.
A username of "Bob" doesn't provide much. A username of "XXXpretty77XXX" provides some. A username of "I_will_fuck_you_all_with_my_big_dick" provides a lot.
If his username affects your judgment of what he has to say
His username is evidence that (among other things) forms my opinion of him. I don't see how it can be any different.
I am? Quote me.
You mistake what ad-hominem, as a bias, is. It is a characteristic of an argument or reaction that is focusing on the person making the arguments, rather than the arguments themselves; the validity of an argument is independent of the person making that argument. Anybody modifying the credibility of an argument because of its source is engaging in ad-hominem. In laymen terms, the term is used to describe an argument against a person, but it is broader than that, as a bias.
...The question is not of "appropriateness". Choices yo
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.