Actually, I earned the nickname thrice, with some variations.
When I first joined engineering college, I had very few friends in my class. Finally, I approached a group of lively looking characters and introduced myself by saying “Hi, I am Atul”.
Instantly one of them (Milind Bengali) turned around and said “A Tool? No, I think you are *The* Tool!”. The nickname stuck, and no one ever called me anything else but “Tool” throughout my tenure in college.
In second year engineering, one of the lectures was about various tools and their usage and maintenance. So the lecturer started with “To cool the tool…” and that brought the house down – I was notoriously hot-headed in those days.
When I started working, I used to quickly write a small utility whenever the need for one arose in my work. This earned me the nickname “Tools” from people who knew nothing about the fact that I had almost the same nickname in college!
Then, when I moved into the online world, a friend of mine by the name of Ashish Gulhati decided that Tools was too tame a spelling, so he re-spelled it as Toolz. This quickly spread through the BBSs and online services I frequented, and so the world now calls me Toolz.