Billie Eilish knows this lesson all too well ... you want to make your fans happy, but there's a line they can't cross.
Billie arrived at JFK Airport in New York Saturday, and some overzealous fans got way too close and frenetic. Her 2 bodyguards had to stave them away ... as the singer traversed her way through the terminal.
Billy's only 19, so the drill isn't old hat ... it's really a dance. When do the bodyguards step in and when do they leave fans to interact?
There were other forms of protection as well, in the form of face masks ... something folks are required to wear in airports ... btw, with the new variant, masks aren't going away any time soon.
Billie's definitely got protection issues ... she's gone to court for a protective order against a man she claims has been harassing her and is potentially dangerous. She claims the guy has been lurking at her L.A. home and bombarding her with threatening letters.
According to the docs, Billie says she got a note from the man saying ... "You can't get what you want, unless what you want is to die for me ... You will know that soon the water will rise, and you might very well die ... You will die."
The LAPD is investigating but so far, no arrests.