Guilty Pleasures

What, exactly, defines a literary guilty pleasure?

I know they exist, at least insofar as there are books I'm frankly embarrassed to admit I've read (no, I will NOT name names, so don't ask...publicly). But I'm not sure where the line is drawn between "fun, light read" and "guilt because I read."

 Guilt because you're reading about pleasure is another thing entirely.

Is there such a line?

I think for me personally, it starts looking pretty well-defined when I know that the book I'm reading is failing at things I value--or at least claim to value--in the things I read.

When the characters are incredibly wooden, the dialogue doesn't ring true, and the prose itself is just bad, I know I'm reading guilty. Same if I fundamentally disagree with an author's worldview (let's say the book is relying on gender normativity I usually find disgusting, say--that happens a depressing amount).

Another good gauge is whether I'd be embarrassed for a subway stranger to see the title, for any reason not yet listed.

But as much as I recognize that I personally seem to perceive this line--that I feel embarrassed of some books I have not only read, but couldn't put down--I also have trouble with the idea that anyone, anywhere, should claim that it exists.

After all, if something is a total page-turner, isn't it achieving something, literarily, even if I think it's bad writing? 

 Plot has never been my strong suit. I have, in fact, been accused of not having any plots in my books on more than one occasion (there's a reason those books didn't sell).

Isn't it just snobbery--worse, ego-driven snobbery--for me to look at a book that nails plot and pacing, but fails at character and style, and say it is automatically less-good than a book that inverts those failures and nail....ures?

Or is there something to the distinction?

I have no answers (frankly, it's straining my capacities just to form these not-that-impressive questions), but I'd love to hear what other people think.

Are there REALLY guilty pleasures? What earns them the label? And what are you embarrassed to have read?