My old username from reddit and HN was already taken and I couldn't think of anything else I wanted to be called so I just picked some random characters like this:

>>> import random
>>> ''.join([random.choice("abcdefghijklmnopqrstuvwxyz0123456789") for x in range(5)])
'e0qdk'

I have that literally in my kbin profile, but it's not on my reddthat one. (I think I tried to copy it there originally when I set up the account but ran into some issue with Lemmy's UI -- been long enough that I forget what exactly.)