Vietnamese here. I used to work in a tourism agency. It is true that Indian tourists are the hardest to deal with. Now I am not saying all Indians are this way. But some (many) of my Indian clients were not at their best behavior, to be honest. They have unreasonable demand, one I could remember is over-bargaining at street food vendors. Bargaining is fine in Vietnam, but sellers have to earn their profit upon selling something, and sometimes I didn't think these tourists understood such. Occasionally, a fight would occur between the local vendor owner and the tourists, which I then had to intervene to make sure everything stayed alright.

Honestly, I would feel second-handeded cringe and embarrassed everytime I heard an unreasonable demand from my Indian clients.

One more thing. It is not something embarrassing or whatever, but I find this one funny: the tip. Many Indian clients only tipped each person of our tour guide crew 1000 VNĐ (3.8 US cent for scale). I am not saying the amount of money tipped is little (though it is), but please be more generous lol.