Fiction writers tend to be people-collectors. We're always on the lookout for quirks, mannerisms, oddities of speech, and so on, so that we can take these things and assemble them into a fictional character.
Which demands the question of whether the characters in fiction are ever completely fictional. I know that for my own writing, most of my characters are patchworks of people I know, or at least have seen. All of them are (I hope and pray) sufficiently different from any one individual that no one will read my work and say, "Hey, wait a minute... that's me!" Still, it's almost inevitable that we construct our characters from what we've experienced.
The result is that I'm always making mental notes of people. I don't try to remember the entirety of a person; I have a fairly dreadful memory for faces, actually, and it'd probably be a forlorn hope for me to try to remember what people look like in detail. But frequently, little details will catch my eye, and go into the mental Rolodex. The elderly woman with the necklace made of large polished obsidian beads. The guy who looks like a member of the Young Republicans except for the complex tribal tattoo on his forearm. The little boy with the cornsilk blond hair and the rather unsettling pale gray eyes. The old man with the face like a bloodhound, wearing a patch on his jacket that says, "I (heart) Jesus." The beautiful young woman with jet black curly hair and a gorgeous figure, who has a laugh that sounds like the bleating of a sheep.
Not all of the pieces ever get fit together into characters; some have to sit a while before I find a place to use them. One of the characters in my work-in-progress, an earnest, kind, intelligent, but rather vague New-Age type, is based in part on a woman I met at a music workshop several years ago. As I said before, she's morphed sufficiently that I doubt she'd recognize herself, but still, my musician acquaintance is definitely the origin of Rainey (short for "Rainbow") Carrington.
All of this is probably going to make my friends a lot more careful around me. It reminds me of the t-shirt I saw -- "Be nice to me, or I'll write you into my novel." I certainly don't mean this to have that effect. Most of the quirks I've collected and added to characters aren't negative, just endearing. In fact, the characters in my stories that are the least like anyone I know are the bad guys -- leading to the (correct) impression that most of the people I know are really awfully nice folks.
Still, I hope you won't take it amiss if you notice that your habit of deliberately wearing two earrings from different pairs shows up in one of my stories. Consider it an hommage to your uniqueness that I (1) actually noticed it, and (2) thought it noteworthy enough to give it to one of my characters. And you have my solemn promise that if you don't reveal the source, I won't.