I pick up quirks from habits that my characters have. I had a character in an rp who said the two C words, Cur and not Cur, and those wiggled heavily into my vocabulary. I started clicking my thumb nail against my middle finger nail when I was stressed, and that was a quirk I gave to my current main character. So I kind of adopt the things my characters do in my writing.
Also, not when writing, but going into the process, (These are really weird!) I stare at my face in the mirror for about an hour sometimes, trying to absorb every detail, and I also touch different parts of my body when I'm thinking of character creation. It helps me understand exactly how I want them to look, and I imagine every single piece of their body that I can. But I think this arises from a desire I have with learning to sculpt or 3D model characters. So maybe I should just learn that. Bt I don't know if my quirks will stop or get worse that way. xD
(Now that everyone knows too much about me, I'll stop talking.)