Fans without any critical sense have bad taste. F.ex. i had a friend who though St. Anger was the best Metallica album ever, even though he had all the other albums. Despite having a huge collection of (pussy) "metal", he will always be a fanboy to me who blindly follows his bands. And if a band released something slighty "heavy" after a calm period of time - it was the BEST ever!.. bah...
bad taste is:
when ppl lack critical sense
when ppl don't have an opinion themselves but needs to be guided
when the only thing ppl can manage to listen is easy listening/sing along music
when ppl who think they have good taste thinks other ppl are idiots for not liking the same
when ppl want to be cool (including teenage goths etc)
Guys who willingly listens to Pink, Britney Spears, Kylie Minogue and even have that on DVD.. What the FUCK are you doing?!?!
But the worst taste is this: Guys (same guy, don't you think?

)who can't handle to listen to music unless it's recorded live in an über düber sound studio with supreme acoustic and supreme sound quality recorded onto a dvd so they can play it on their über düper surround sound high difinition hi-tech 3000 stereo with gold/optic cables worth a fortune, only to hear how well the guitar sound " just listen to the sound quality of that guitar recording, wow, man! cool right?" Yes, you are a fucking morron! The worst thing about this type is they can't handle to hear music or see movies elsewhere "it's not good enough, i might as well just stay home then!"
i also agree with Radagast on the "a little of everything", those ussual don't have a clue on what they are doing. Now i'm mostly thinking about teenagers who say so and old farts who only like metallica cuz "sad but true is a very good song"
i would like to think it's all relative, but it depends on your definition of "bad taste", i guess. By my definition a person who has no interest in music and doesn't know anything about it have bad taste (concerning music), and that's fair enough i think. It doesn't necessarily makes him or her an idiot, unless he thinks i'm an idiot for listening to my music, or not having the right stereo.