Mine is King of Coffeebeans in German.
I didnt like my previous online name cause i made it in a hurry but it stayed around for years, but one day in school we talked about evolution in religion of all subjects and our teacher introduced some different schools of thought, including the guy who said giraffes have long necks cause they stretch so much. I quite frankly thought that was stupid, exercising does not change your gen pool and it didnt cross my mind that you can explain wrong idears for the sake of learning the process how something was discoverd.
But in the moment i was having non of that, argued back with genetics and all and when my teacher said that yeah it is outdated but before we knew about genetics it was plausible i again argued back that aslong as you cant prove something you cant claim it as correct when it goes against the scientific knowledge of your time, as i also cant claim that i got coffee in my veigns and am there for the king of coffeebeans.
And that name stuck and i still like it alot, especally due to the ironic part that i do not like coffee very much.