Mine is simply a deviation of the complete handicapped name I came up with as a 9 Yr.Old online.
I was going to play BattleOn (When it was recommended to me by some friends) and I just named my character "bloople". I later added the word "Master" to it, so for a while, I was "Master Bloople". Although I probably had a lot more o's than that in the name, but I'll keep it shortened in here. :)
After being recommended Runescape by the same friends as before, I created an account named "Master Bloople". I forgot about the account and went back to it some time later. I had forgotten the password though, so I simply made a new name.
I was then known as "Sir Bloople". Unfortuantely the same thing happened again and I realised that I didn't really like the name "Bloople", so I changed it to "Dooble".
I first went back to naming myself "Master Dooble", although I found that "Sir Dooble" was slightly better fitting. (I also think it was a name that woud fit in some game, whereas Master Dooble wouldn't)
After being recommended Blockland by a friend, I got into it, but had a couple of questions so I made a forum account to ask them. I was probably in a hurry or just not paying attention, or I just didn't care, but I ended up with the name "sir dooble", un-capitalized.
I eventually got into spending time and commenting on the forums, and just decided to carry on with the name "sir dooble" and not get it changed to a capitalized version, just for some sort of remminiscence of old times. :3
Although, in-game I'm still "Sir Dooble", however in some games I'm "Master Dooble".