Sane vs. Eccentric vs. Insane

I question my sanity... on a pretty regular basis.
Is that a bad thing?
Who dictates what's sane and what isn't?
Where exactly is that fine line that separates eccentricity and insanity?
When do one's actions stop being silly and odd and become full out problematic?

Now don't get me wrong- I'm not a full blown quack and eccentricity does run quite strongly in my family (stemming from my Grandfather in particular who is literally a linguistic genius); however, I can't help but stop and think when someone proclaims how crazy I am if perhaps.. they're right? Wikipedia portrays eccentricity in a positive light stating that:

"Eccentricity is often associated with genius, giftedness, or creativity. The individual's eccentric behavior is perceived to be the outward expression of his or her unique intelligence or creative impulse. In this vein, the eccentric's habits are incomprehensible not because they are illogical or the result of madness, but because they stem from a mind so original that it cannot be conformed to societal norms."

This perspective would explain why my Grandpa and Mom are the way they often are and have yet to be institutionalized (*KNOCK ON WOOD* It's a joke!), and it even makes me feel a bit better about my own "out-there" ways and thoughts about life.

Interestingly, Wikipedia also states that being the eldest child can often lead to eccentric behaviour as a way for the child to try and stand out... Both myself and my Grandfather are the oldest... There's very few people that I actually let see the real me, reason being that I'm afraid they'll think I'm crazy... why am I afraid of this? If I was crazy then shouldn't it be them that are afraid of me and not the other way around?

Who knows... I could talk in circles about things like this; but the point is:

What IS sanity? Does sanity mean conforming to those around us so as not to stick out and "be different"? And really... who dictates when you've crossed that gray line from eccentricity into full blown insanity? I guess I should be grateful that I'm potentially eccentric due to the fact that Wikipedia associates it with giftedness of sorts...

Anywho, those are my thoughts. Had to get it out cause I've been called crazy quite alot this week and it's really got me dwelling about what it means to be crazy in the first place...