This may sound crazy, or like I’m making it up, but a couple of people I went to high school with would sometimes amuse themselves by going somewhere, and sitting motionlessly as they could, and stare at someone. They made wagers beforehand over how long the person would take to move out of sight, upon spotting them. And kept a diary of who, where, when, how long, and how much.
They said they liked the challenge of trying to pick who would freak out easily, and who would try to be stoic about it. They also liked that eventually, everyone got pretty uncomfortable, and moved.
They were actually pretty creepy even in “regular” mode, come to think about it. I never accepted a ride home from either of them, even if other people were going with them.
On that last one, it was sort of a “thing” at my high school to give a lot of people rides home once you got a license. I did it too-- I would choose to drive my uncle’s 72 Chevelle that needed transmission work, over one of the smaller, newer cars, because of the number of people who could fit into it (before seatbelt laws).
These guys wore a lot of black, chains, leather, and skipped class to play tabletop games.
Without intending to, I always pictured them when I read anything about the Columbine shooters.
The staring thing was interesting, though; it makes me wonder if the couple in the OP were trying to be creepy on purpose. At the least, they may have been people who lost a bet, or picked “dare” in a game of “Truth or Dare.”
Now, I’m sure they would have loved knowing people were really creeped out by them-- obviously, they were trying to cultivate it.
One of them was honest-to-gawd named “Thanatos.” That was his real name. His mother made really weird junk art. So weird.
I ran into one of them about 6 years after graduation. He owned, and used as his everyday car, a vintage hearse-- late 50s, or early 60s.