There are three levels to this.
1) I trade Bitcoin.
2) I'm a long term investor
3) I'm a Bitcoiner
I've seen plenty of people vacillate between 1 & 2.
I've never met someone who used to be a bitcoiner
Discussion
When you consider someone being "Bitcoiner"?
Your a bitcoiner if you identify as a bitcoiner
Generally I would assume this is when you realize what bitcoin is beyond "number go up". You are right there is no returning from that state.
Labels could be dangerous thing. Bitcoiner is label attached to you. I would rather love to be called person with common sense or person with his own integrity.
In spirit of promotions of Bitcoin it's fine but... Think you understand.
The official initiation ritual is to do this at your PoW:
(Place of Work)
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*ahem* I mean, “Bitcoin”
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In my view a Bitcoiner is someone who buys Bitcoin not to ever sell back for fiat, but to hodl (like in a savings account) and (in future, when needed) only will spend Bitcoin for goods and services. That's what I do anyway.