Mine is one I've used in online dating profiles. I wanted something with good contrasting elements to it. I used variations of "Adventurous Spirit" for a while. Now I have ClassyCaveman and one other similar one that I use but I don't want it to get stolen so I'm not willing to share it here!
I hate usernames with '_69' or something similar on the end. ... With one notable exception: My best friend has alphaone69 which is friggin awesome.