First, I am so sorry that people were so incredibly rude to you while you were on vacation visiting your hometown. I'm sure this could have happened in any country but I wonder if some cultures are more blunt than others. I know that is true in China, as I had sales people shoo me out of the store, telling me they didn't have any shoes or clothes to fit me.
Second, the dress looks fantastic on you and I'm glad you bought it. I bet your confident, happy energy threatens these insecure women (are men just less rude in Italy?). Fat-shaming you may have been a petty way to burst your bubble. We should celebrate and admire confident, happy people, not try to tear them down so they can join us in our misery.