For me...
The Carlton Towers in London about a year before Hyatt sold it. It was getting quite run down then, even in the public areas. I remember seeing chips of tile falling off in the swimming pool. Ugh!
The Hempel in London. What a horrible idea for a luxury hotel! It was designed by and I'm assuming for bored rich Londoners who were looking for something new no matter how ridiculous it was. 600 pounds per night for what?
I only tried the Crillon in Paris once and I didn't like it very much. It was way too snooty and I guess I was too young for that attitude. The Lancaster is far better in every respect.
As for the Grand in Stockholm, most Flyertalkers know that when you get to your crummy room, don't unpack. Go right back down to reception and complain and you will get a great room. This really is the best hotel in town in most other respects.
As for Cannes, the hotel owners have been living off reputations for over 100 years. The Martinez was tops back then and it still is. I used to like the Carlton a lot, but when I-C took over it became a convention hotel.