"caird coinheringaahing" comes from this Jelly answer. Given that the answer is written in Jelly (my primary language on the site), and the challenge is very much about the site, I thought that it'd be a fun, unique username that references the site.
And it should be pronounced "cared co-in-hear-ing-aah-ing"
Fun fact, moving the space around in that answer leads to the following possible usernames:
ChartZ Belatedly oppS,aback reerects bespangling aachen Erasmians cleptaahing caird coinheringaahing Dude coinheringaahing I have changed my username (briefly) to both ChartZ Belatedly (during March 2021) and Dude coinheringaahing (August 2021), and I'm reerects bespangling aachen on the CGCC Gaming Discord server.
During June, July and August 2022, my username was "Zion mycelia adamancy", as requested by emanresu A due to this message in TNB:
6 hours ago, by Radvylf Programs
Well my Jelly encoder doesn't quite work yet, unless caird changed their name to Zion mycelia adamancy! and none of us noticed
As for my avatar, it is a picture of my adorable puppy, Patch. Over December/January, I put a Santa hat on him.