scopaesthesia

The proposed ability of a given human being to detect they are being watched via extrasensory means, also known as the "psychic staring effect". It could be argued that it only applies when said feeling is accurate, and it's hard to test whether this is a real phenomena or simply paranoia turning out to be true sometimes (a broken clock is right twice a day).

Fred: "Man, why can't I ever sneak up on you?"

Johnny: "Scopaesthesia, Fred - I already knew you were there."