The worst I had just a couple of weeks ago, in a Hot Biscuit off the north Houston freeway. The "philly cheesesteak" was a baguette, with some cremated pieces of meat that still managed to smell strange in it, along with some too obviously fake cheese.
To complement this fabulous piece of cookery came soggy, fatty chips with no salt or other seasoning on them.
The second worst I ever had was the "ultimate cheeseburger" at jack in the box. Why the flying fuck I decided to go to jack in the box in the first place is beyond me.
WHAT. Blasphemy. Although I'm sure you can get shitty paella in Spain too, but holy fuck is it good when you get the good stuff, which is just about anywhere in Spain. Which city was this in?
Also, you should go to Japan and ask for dancing shrimp. Really, trust me on this.