For me it’s probably a tie between my best friend from college, my baby sister, and my former therapist.
Currently Sis is slightly ahead. I lent one of our nieces my debit card earlier so she could do some shopping for a family dinner, and when my niece asked for the PIN, my sister told her it was probably one of 4 sequences: the first four digits of Avogadro’s number, pi, Planck’s constant, or e. She was right. I’ve never told her how I choose my PINs; she just knows that’s what I think is easy to remember.
But I don’t doubt my college friend could have made the same deduction. She can also predict, almost infallibly, what I will order if we are visiting a restaurant new to both of us, or what movie I’ll choose to see, or whether I’ll like a given author.
(Athena help me if the two of them decide to join forces and whack me. I’d never escape.)
Of course, my therapist knows things about me that neither of them do, as I do not discuss sex with my little sister.