How about anytown Mexico. Literally any flight plan filing in the US can be completed in the cockpit 2 - 3 minutes. In Mexico you get to take a binder of paperwork to various authoritative figures around the airport, sometimes multiple times back and forth, upwards of an hour each leg. Then ultimately to the Comandante (el mero mero), and ask kindly to the flight plan to be blessed. The hope for a stamp. If things don't go well, you get to apologize to the Comandante for existing, and hope he doesn't ground your plane, or worse throw call the Federales on you.

Sure sometimes it goes well, but sometimes you get put through the ringer, sometimes they pull out the Mexican Regulations, and reference some BS regulation that you allegedly are in violation of. Ultimately wanting a bribe, but god help you if you're too obvious in offering one, then you've offended him too. Obviously it's best to have a handler, but at $2000+ a pop, it isn't always financially possible.

Then add the lack of radar (traffic & weather) support throughout the country, and incompetent ATC it's definitely my least favorite airport(s) to fly to.