I used to have longish hair, and aft slating someone's receding hairline during a round of insults during poker, his retort was that I had a legohead. I removed the 'A' and use it in a lot of forums.
MrClean came about many, many years ago because I kept my car so clean, all of the time. My family, friends and co-workers called me this, and it stuck.
It was a notable thing considering central Ohio gets about 39" of rain per year (same as Seattle) and only 100 sunny days.
Later, I lost my hair and now I look like MrClean (shaven head).
Mine started 10+ years ago (ATV forum) - after numerous GTG camping ATV trips (lots of drinking in the evening), I picked up Mofo, as being a crazy mother*******.
Later on I added G23 due to Mofo already being used on some other forums (Glocktalk) - G23 being my favorite hand gun.... so this user ID has followed me everywhere since....
started using it 3 years ago for various car and audio and other forums and didn't want to add anymore user id's to the already way too long list. 1st new app for my Droid phone was a password safe for that very reason (BlackBerry came with one), I still have a good memory at 59, but not that good..