Easy...Jamaica (as almost everyone else agrees). Why?
1. Filthy. One of the dirtiest places I have seen in the world. Come on people, pick up your stinking trash. The world is not your garbage can.
2. Rudeness. People selling items getting verbally agressive when you tell them you don't want to purchase their overpriced crap.
3. Bait/Switch. Cab drivers that will not leave you alone. Actually took one up on a short tour once. At the end of it he trippled the cost. Figured that it wasn't worth arguing about, as I didn't want to hike 7 miles back to the boat.
4. Dope. May be your thing, but I hate getting it shoved at me all the time. And I love the federalies who- in broad daylight- sleep on the pier under the signs saying that you will be arrested for bringing/taking narcotics with you.
4. Denial. I love how all the 5 start resorts seclude themselves from the rest of the country by either a) brick walls, or b) folliage. Even they don't want people looking out and seeing how dismal of a place Jamaica is.