My current username doesn't have a long history, so Imma recount the legends of my entire username history instead 
So during early days, I went by ctang15, because it was my student ID or school email or something. Simple enough.
But of course that was boring, so I wanted to change it. Being a frequent reader of TvTropes at the time, I stumbled upon the trope A.I. Is A Crapshoot, and my first thought was "heh heh, 'crap'" (I was very mature) and my second thought was "what the heck does 'crapshoot' mean anyways"? So I looked it up:

Being a quiet autistic kid who didn't get into much trouble, people would say I was organized and obedient and liked routine, and I HAAAAAATED this reputation. I was too shy to rebel against it openly, but in my head (and on the internet), I was like 'no, I'm CHAOTIC and RANDUM' and so I started going by crapsh0ot (with a zero because 'crapshoot' was taken :P)
Then later, I got into math and wanted to start a math channel, which I named TheLemmaLlama (a 'lemma' is basically an oddly specific theorem that has no interest or use beyond proving a more interesting theorem, and it sounds kind of like 'llama')
I'm no longer interesting in being a math youtuber, but I still think the handle is neat, so I've decided to keep it 