It can come off as creepy if you know a lot about a person, but that doesn't necessarily just come from FB stalking.
For example I have a friend who has an extremely good long term memory , he can recall the smallest details about the most insignificant events and conversations that happened many many years ago. He also basically carries an encyclopaedia of trivia around in his brain.
He eventually learned that he had to pretend to be dumber and more forgetful to avoid being thought of as creepy and pedantic.
She was teaching (as a grad student) and realized on the first day of class that she already knew the names of almost all of the students in the class, and little bits about them, from random encounters (like "I was sitting behind those two on the bus a few months ago").
She pretended to be learning their names, anyway, because that's just way too creepy, as you said.
Her memory serves her well in life; she writes fiction. She's also really useful for me to have around -- I have a terrible memory for data I'm not actively using (possibly due to lots of general anesthesia as a kid...), so she remembers tons of things for both of us.
For example I have a friend who has an extremely good long term memory , he can recall the smallest details about the most insignificant events and conversations that happened many many years ago. He also basically carries an encyclopaedia of trivia around in his brain.
He eventually learned that he had to pretend to be dumber and more forgetful to avoid being thought of as creepy and pedantic.