Mine's ridiculously obvious. xD
But then, in a longer version of the same reason, I s'pose it's because of WoW. Haha. I'd wanted a different name when I signed up for it way back when, and apparently it was too short. So my sister just used 'yoshirules', since I've always been pretty crazy about Yoshi. It stuck.
And lard, am I glad it did. I can't imagine not being Yoshi now. Just to think.. if I were tashahi instead of yoshirules, the Yoshilisk wouldn't exist. I wouldn't even have my love of green! 8(
'S a scary thought.