I just checked out the relatively new Fatt Dog location on Market slightly west of Montgomery (in between the McKesson building and Lee's Deli). In a nutshell, the dog itself is good, the toppings left a lot to be desired. Perhaps it was a case of caveat emptor.
Opted for a double Chicago dog. This sort of out-of-the-box thinking threw them for a loop ("Hey guys, I've got a new one for you--a Chicago dog with an extra hot dog."). They have only one kind of bun, and it's big, so a single dog gets lost in it.
Dogs appeared to be pre-cooked and then reheated on the grill. They had a nice little char and a decent "snap." Long and skinny, they stuck out of both ends of the bun about an inch.
As for the toppings. Ummm, to the folks at Fatt Dog, do your research. First, you need some yellow mustard. There was none, although I think there was a wafer-thin smear of some tasteless brown mustard. Next, try to source some good fluorescent green relish. Then, don't use wedges of mealy, overripe tomatoes, use half-slices of ripe tomatoes. While you're sourcing the right kind of relish, see if they also have some sport peppers, instead of a mushy pickled jalapeno. Finally, go for the Clausen-type pickles, not the Vlasic-type pickles. If you can find some celery salt, . . . .
That said, the hot dog is good, and I'll go back to try the sausages, which will probably be a better complement for the large buns.