I agree with the buffets. It was a buffet (at a popular US casino) where I obtained my only bout of food poisoning many years ago. And I'm surprised with all the places I eaten at and strange things I've eaten over the years living in Thailand and China that I haven't gotten ill again.
You've never been to a Dunkin Donuts or Mister Donut where it was 'help yourself'? Or at other places where French breads and other bakery items were in bags not completely closed?
......and to add, you never received a polio, measles, chickenpox or other vaccination? If memory serves me right I had to obtain a Yellow Fever vaccination many years ago (more than 30) when I first came to Thailand on a Business Visa.