For people my age, taste is a personal aesthetic code. Good taste can be idiosyncratic, in fact, it's expected to be. You're supposed to like what you like for your own well-thought-out reasons, and not just like what everyone else likes. (There are also shared cultural and class standards of "good taste," but those aren't what I'm talking about.)
Someone with taste has a well fleshed-out theory about what makes a work of art good or bad. The cultivated observer is supposed to be able to see something new and rigorously scrutinize it according to their code.
That's why people who put a lot of stake in their own good taste are so delighted when they discover a brilliant unknown band in a seedy bar. By recognizing brilliance in unpromising circumstances they are demonstrating that their aesthetic judgements are uncontaminated by extraneous factors like whether the band is popular or heavily promoted.
Having coherent reasons for your preferences is integral to the concept of good taste. You're supposed to be able to recognize a band that swings hard, or a rocking baseline, or witty lyrics, or whatever you think is important in music.
You gain status for your good taste if you can reliably pick stuff that other people will like. You can't be capricious. If you recommend songs strictly because they have sentimental value for you, they're unlikely to appeal to other people. You have to appeal to shared musical values.
"Guilty pleasures" are things people like but can't justify liking. The concept of a guilty pleasure only makes sense if you try to live by an aesthetic code in the first place. If you just like whatever you like, for any reason, or no reason--you don't have guilty pleasures. If you can admit that you like a song just because it was playing while you lost your virginity, the concept of a "guilty pleasure" is irrelevant for you.
A lot of people who aspire to have good taste won't admit that they sometimes like songs for "irrelevant" reasons. It's human nature to enjoy music that you associate with other pleasures. Sometimes you love a song because the singer is pretty, or because it was a number one hit the summer you drove across the country, or because it has become soothing by sheer repetition, or because it's your best friend's karaoke standby and you love her.
[Photo credit: Roadside Pictures, Creative Commons.]