Honestly, back in the day they told you not to judge but I've found a good solid 95% of the time I can judge someone and be completely correct about them. Hell, on this website alone I can generally look at someone's avatar, signature, location, and their title to get a fair of idea of their real personality.
Example, somebody with "darker" anime imagery and and a naming convention like Dark, Shadow, etc coupled with their location as something like "Darkness", "Void....." etc, I think it would be fair to pass an accurate judgment that they are someone trying to be a non-conformist goth in high school (although how these goth kids reject all mainstream ideals with the same ideas as each others and act, dress, basically carbon copies of each other makes them non-conformist is beyond me, but okay).
Or another example, people with a numerical naming convention (such as Genericname42) that type with a lot of emoticons and use acronyms like ofc, tbh, nel, etc. tend to be foreign teens, simply because I've encountered few Americans in the online community that use ofc and nel as acronyms.
Please note, mods, that this is not a trolling topic but rather discussions of stereotypes that do represent accurate judgments of someone.