From the thread title, I thought this was going to be about "shameful" books on the actual TBR that one was embarrassed about going-to-be-reading: i.e., guilty pleasures and really trashy mind-candy stuff and dubiously-erotic semi-porn.
I personally don't keep much in the way of a TBR ("what's due at the library soon" and "I should read this freebie/cheapo I already have to decide whether I want to buy more in the same series/by same author before I spend more actual money on the time-limited tie-in sale" is pretty much it).
But I do have umpteen dozen assorted probably-trashy occasionally-erotic romances both gay and het* which I picked up really cheap on sale† even though I'm a generally a no-romo non-romance reader, which I should probably read through at some point. And I've also a whole bunch of retro-pulpy sci-fi/fantasy/crime as well, though I'm hoping for somewhat higher quality on those, since I tend to pick them on criteria slightly more meaningful than "well, this plot synopsis sounds cracktastic enough to be entertaining for < $2" and "my ghod, now I have to see just how wacky the author's drug trip got" .
* Nothing bi, alas.
† They were really cheap! And DRM-free from a small specialty business/publisher which I wanted to support! And I was morbidly curious! And I generally like stuff with time-travel in it! Even the cheesy kind of pop-culture rip-off time-travel with trusty hedgehog assistants playing Cupid!