My forum name: I was really into WWE and wrestling, and combined the names of Jeff Hardy, and Rey Mysterio's finisher move, the 619. Together, I made it Hardy619. I had already had the username wen I had played Roblox, so I just carried it over to Blockland.
In-game name (Lavasoft): There was a video I saw long ago called "Lego Runescape". The main character in that video used the name Lavasoft. I liked it, so I took it and that's my name now.