Tönz, I saw a graffiti painting with that name in Poland last week.

Anyhow my nick started out as AtomVinterNatt (Nuclear winter night) which is a song by the swedish punkband Dia Psalma. I used it when I played onlinegames and quickly changed it to just atom since it's shorter and faster to write.
I chose it because it was the first thing that came to my mind, and I really liked it.
Nowdays everyone calls me that, friends, theire parents and my teachers did it when I went to school.