When I was in high school, Fleetwood Mac was just dreadfully un-cool... even when 'Tango' was big.
FM was either the band that your mom and dad listened to, or your kid sister listened to.
Most rock/classic rock fans tend to think of FM as a "soft" band, lacking the crunch and electricity of bands like Led Zeppelin, Aerosmith, Van Halen, etc.
And they're often considered too AC for the Top 40 crowd.
It's funny though, for as much grief as did (and still do) get for being an FM fan, many of my friends in high school would say, "hey, I saw FM on MTV this weekend," or "I heard Stevie's new song on the radio."
Sometimes they'd even admit to liking it.
But I have converted many, many people over the years. I gauge what kind of music they tend to listen to, fashion a Mac mix-tape (or, now, CD) to suit their tastes, and then let the music do the rest.
I've found that once someone has a few Mac songs they really like, they tend to be more open to the songs they might not have listened to before.
Still, it doesn't work on everyone... my father & brother especially! (Though Dad usually likes Christine's songs and loves "Tusk," and my brother "tolerates" "Never Going Back Again.")