h, I can't resist.
My all-purpose, always-available, mostly-unique login, 'psydid', is nothing more or less than a random word that I chose back when it appeared that the number of logins I was using far exceeded my poor mental capabilities.
I keep bouncing between my real initials 'pwm', my college email username 'pwm5', my preferred pseudo-initials 'pmc', the pretentious-yet-ancestor-aware version of same 'pmc xvii', my first name alone (always lower-case, as I still like to use in small & homely namespaces). Or I would forego all of these and pick a crafty but anonymous moniker like 'posterboy' (useful on Usenet).
Eventually I decided to stick to a name that would be near-certainly available wherever I requested it, and since I was on some kind of mutant-telepathic-power kick, I used a variant of 'psi' as a prefix and a random syllable as a suffix. It's efficient & distinctive, and I've become somewhat fond of it online, though I've never felt quite comfortable using it aloud.