Two come to mind...
My favourite chocolate bar ever was Dime. If you've never had it, it's a slab of croquant (hard, glass-brittle caramel with maybe a little fine-ground nuts in), covered in ripple-y milk chocolate. Could hardly be more decadent, I suppose, solid browned sugar at the centre, and then thick milk chocolate on the outside! I would scrape, borrow, steal money, because my allowance was already gone usually, and then buy like three double bars at a time. I preferred them frozen, probably since I'd hidden them in the freezer at some point, so I would pop two of them and half the first one in there, and start eating the first half sitting on my bed, usually reading a comic book. I had a specific way I had to fold the duvet behind my back and got stressed out if everything wasn't perfect. Once the first half bar was gone I had to immediately go and get the second half, even though it wouldn't have had time to freeze all the way yet. It didn't matter to the sugar monster in me demanding FOOD. NOW. Once I'd finished that one the others would be cold and stiff enough to shatter when bent. Lovely. I would finish the second whole bar, and then start panicking because there was only one double bar left, and after that one I would have NOTHING! Though of course, that one followed the first two in short order, and then I started plotting how to get more money for more chocolate next time.
The second also involved milk chocolate, come to think of it. I was a teenager by then. I'd discovered that plain milk chocolate came in 200 gram bars, and that it tasted lovely if mixed with a little fat (actually I mostly used margarine, not even butter, *sigh*...), and then frozen. Yes, developing a theme here! I would then sit in front of the TV with a litre measuring cup filled with a solid block of chocolate and hack out chunks with a butter knife until the block was all gone.
I have others, but these were the most guilt-inducing.