I can pretty much have some form of meaningful music conversation with anyone. When they say "Oh, I like everything" it's usually more like the Blues Brothers quote "Oh we've got both kinds: Country AND Western!".
My "everything" is usually a bit bigger and often contains at least some of the music they like. I know the difference between Beethoven's middle and late string quartets (I have the sheet music, too), I can tell you why Necromantheon is the first band in years to GET Thrash Metal, I can (or at least could) play several of Dave Gilmours guitar solos half convincingly, and I know why Hamza El-Din is considered one of the finest Oud players. I can talk about Azeri composers (Isn't Fikret Amirov's Nizami just devine?), and I saw Miles Davis in concert (oh f*****g YES!). I love black and death metal. Even the church burning satanist s**t (I AM Norwegian, after all), but I don't paint my face like a corpse to go see Satyricon or Immortal...
My biggest holes would have to be Hip-Hop and rap, although I have and like some albums (and Lauryn Hill at the PinkPop festival in 1999 is on my top five gigs ever list). I once owned every Frank Zappa album ever released, minus the original pressing of Läther.
I could go on, but I hope my point is made. I love music.
But I really hate being asked the question, because frankly, I'll never be as fluent in any of these as the devoted monochromatic fans.
And I hate feeling superior. Because I'm not.
Genres are useful for talking to the one-dimensional, and for finding new music. But mostly I differentiate music like this. Good Music and Shite. Motorpsycho is Good Music, Tone Damli Aaberge is shite. Simple, really.