In my opinion, nothing tops GUESS as the worst advertisement currently out there.
Once upon a time, it used to use great models (Claudia, Josie, Alessandra, Bridget, even Anna Nicole when you look back), it used to have simple, yet captivating settings and situations (Drew Barrymore sitting on a lawn chair, Claudia coming out of a bar, Laetitia dancing with a group of people, Josie Maran sitting alone on a dirt road), and it used to have simple, but totally sexy close ups (the one with Carre Otis wearing a bandana and hoop earrings comes to mind)...
... but now we get unknown models (I'm sorry, but who exaclty is Melissa Haro?) or trashy celebrities (Paris Hilton), UNIMAGINATIVE settings galore (oh, the beach... again? a bar... again? on top of a convertible... and on top of a motorcycle, done and redone till there is no tomorrow. And don't get me started on the "lesbo" scenario that appears in at least one out of two guess ads. And let's not forget the overly cosmeticized girls with dark eyeshadow and bee stung red lips that end up looking like drag queens or strippers or p*rn stars or all of the above.
Trashy, boring, and over.