When you stay up all night making five different versions of your code.
When you get giddy over the idea of setting up programming environments.
When all you talk about, to the point of your friends avoiding you, is FIRST.
When you post in threads about OD'ing on FIRST
When you rewrite your Drive code about fifteen times because it isn't pretty enough....
Edit: One more: When you read the javadoc in your free time...