I got my username through kind of a complex process.
It first started as "cvieyra." It's the first letter of my first name mixed with my last name, "vieyra" (see-vee-air-rah). This was back in 2011, February.
Later, in 2014, early March/Late February, they added chat for people younger than 13 (I was 11/12). But the filter was really harsh, so to escape the harshness, I made an alt account called "Cvieyra1test." I later forgot the password (I think).
So then I created "Cvieyra2test." Which would last for about a year until mid-2015 when I was having issues with the Roblox site with accounts not logging in properly. I made "Cvieyra3test" and "Cvieyra4test." Both of which I've abandoned since after I was able to log back into "Cvieyra2test."
I've stayed with "Cvieyra2test" since, due to its catchy name, "see-vee-air-rah-two-test."