That's a weird assertion, because if you're driving a Tesla and using autopilot/TACS you have to use turn signals to change lanes.
I've seen hundreds of Teslas driving in the UK and they're just as likely to use a turn signal as anyone else (~99%).
I'm not sure I've seen a less substantive comment on hacker news that wasn't flagged.
People in the UK actually use their turn signals. Try driving around Central Texas. The joke, as another commenter pointed out, used to be BMW drivers. There is some kind of linear relationship between the luxury of a car and the lack of conscientiousness amongst many American drivers.