Oh, and I’ve heard Minneapolis/St. Paul called “The Twin Shitties” before.
It strikes me how so very few of these approach anything near clever.
(although Krap Room ain’t bad) 
mmm
Some Texas ones I’ve heard:
Fort Worth --> Fort Worthless
Waco --> Wacko (the Branch Davidian/David Koresh reference)
Euless–> Useless
Houston–> Pee-yew-ston (a reference to the petrochem/refineries that give some areas a pretty unpleasant stench)
One derogatory nickname that was rechristened into something a little more dignified, was the downtown area in Fort Worth, that was long known as “Hell’s Half Acre” and is now known as “Sundance Square”.
Or for extra flavor, Dirty Rottenchester.
Years ago, the small town down the road had a onion-bulb style water tower, earning it the nickname of “doorknob to the shithouse of the world.”
(bolding mine) Foxnard, or Da 'Nard.
Here in the Bay Area: Berserkley, Hayweird for Hayward, Milpenis for Milpitas, Funnyvale for Sunnyvale.
Rolling Ghettos for the Chicago suburb of Rolling Meadows.
Near Chattanooga is a small town that used to be two smaller towns, Soddy and Daisy. Of course, the name Soddy Daisy is bad enough. But when I was growing up, the place had a reputation for having particularly scary rednecks (think Deliverance). Thus, we called it Sodomy Daisy.
Birmingham, Alabama’s nickname is “The Magic City” but some refer to it as “The Tragic City”.
A friend of mine calls Starkville, Mississippi “Starkghanistan”.
Vitoria/Gasteiz is also known as Siberia/Gasteiz, due to its climate; it’s not so much derogatory as a warning to first-time visitors. I’ve seen snow on the ground there in July.
Students at the Universidad de La Almunia refer to that little town as LA, pronounced in Spanish, and follow it by a speech on how it is very much not the same as LA pronounced in English; quite the opposite.
Made me laugh out loud.
Which is saying the same thing three different times. 
We called Rochester “Crotchfester” and Syracuse “Zero-cuse”.
Then there’s the Mistake by the Lake a/k/a “Barfalo” or Buffalo.
Poughkeepsie was often called “Puke-Upsy”.
Don’t forget Tupperware Lake (Tupper Lake).
And, a bit to the east, Vermonters refer to the state capital, Montpelier, as Montpeculiar.
I’ve lived in Folsom (a Sacramento suburb) for 14 years and I don’t think I’ve ever heard it called “Sacratomato”. I think I’ve mostly just heard it called “California’s biggest farm town” and “The Midwest of California”.
In ID we have poke-n-tell-all, er pocatello. While I don’t know personally, I’ve been told by folks that grew up there that it’s a pretty accurate name
Chicago - “Chiraq” because of the violence.
When we last visited Costa Rica the nearest town, Tamarindo, was referred to by the locals as “Tamagringo” because of the high concentration of American ex-pats. It made me smile…
I call Seminole “So Many Old”
St. Petersburg = St Peter’s turd
Orlando = Whorelando
Pinellas Park = Penniless Park (very fitting)
Inglewood, CA = Inglewatts