I used to be into punk rock and rock until only about 3 years ago until I discovered In Flames which got me into the whole scandinavian thing then I found out about CoB when AYDY came out (Though shortly after I discovered Hatebreeder and FTR, AYDY probably didn't get played for a year because I was so addicted to those CoB albums).
Now I listen to anything from thrash metal, death metal, black metal to progressive. Some people just need to find out about bands and you'll be surprised how much people can change. Heck I didn't think I'd be listening to the shit I am now 4 years ago. It seems like most metal people don't want people to find out about awesome bands, they just keep them all to themselves like a secret. Which isn't a bad thing I suppose
, I do try and get some people into metal sometimes though by recommending some easy listening metal (Like Melodic Death Metal or stuff with singing)