This is my silliest. It came up during a poker game with some chorus buddies, and one of the guys joked that I slightly resembled Bonk from Bonk's Adventure, so the name stuck (Bonk). After a year or so, I modified it a bit in order to make it my own (Bonkus Maximus).
Prior to that, I had three gamer tags, all starting in 1998: _Junk_Yard_Dog (in homage to professional wrestler Sylvester Ritter, who had recently died), CDL_Undertaker (I started my online gaming playing Star Wars Rebellion and joined an Imperial aligned clan), and AOD_Archon (When I started playing X-Wing vs. Tie Fighter online, I ran into an AOD_Undertaker)