Uh, mine is kinda random and is sorta based on inside jokes, I guess? But, back in 2013 I wanted an interesting username because I was gonna join DeviantArt for the first time and I was trying to come up with something. There were these robotic enemies in one of the Mario Bros. games that I called robocheatsies and that came from some Mario character that had a name like "Cheatsy" or something like that. As for the TM part, well, I had my art stolen on DA once and got paranoid about copyrighting or trademarking everything in case something got stolen ever again. Now I realize I really don't need it, but I've grown so used to putting "TM" in the name that my username looks weird to me without it! XD
Edit: Also the name "Kazumi" comes from the name of a VA I liked a lot back when I was really into MLP (she was always so nice to my dorky self back then, too). Then in one of my Pokemon games I named my trainer "Kazumi" because I wanted a cool name and really liked the way "Kazumi" sounded. I ended up changing my name on YT to Kazumi because I grew kinda tired of using RoboCheatsy for a while since I'd been using it since 2013. Now I use "RoboCheatsy" when I need a username kinda name, and then when I need a more "normal" name, I use Kazumi!