Mine is steve for my first name and d for my last name. But back in the day I had to create a work account for eBay and steved was already taken, and every other good combination of my name was taken. So I picked steved with some hexidecimal characters after it. I can't remember what they stood for (maybe my phone number at the time with ended in 7878) but the main benefit was that that name was available everywhere. I eventually shortened it to steved0x, which also is never taken anywhere
Now I write technical documentation, and so people think it means steve docs (with d0x for docs), which works out