I have a list that's way too long but one overseas destination that was particularly bad imo is Langkawi Island, Malaysia.

It's the prime example of pristine beauty destroyed by tourism and urban sprawl. The amount of litter is just shocking on their beaches. Add to that the amount of people that are being ferried in and out of the island, it's just sad. Too many vendors on their streets and the best views of Langkawi Island are spoiled by the fact you need to be a guest of their ultra expensive 5-6 star resorts. The boat ride and the airplane back to Kuala Lumpur were the best parts of my trip there.