By this I mean the overstimulation of the senses that happens while you are there.
My answer is probably Old Delhi. From the sheer population density, the near-constant honking, the utter chaos on the streets, the panoply of religions and ethnicities, the myriad scents and colours that pass you by as you travel down the narrow lanes, and not least the choking air pollution, it is certain to keep you on edge, not necessarily in a bad way.
Are there other cities that come close to, or even surpass, this?
Off the top of my head: Delhi Istanbul Hanoi
I wouldn’t say Istanbul rates compared to Delhi and Hanoi (or much more, Saigon). It’s downright orderly and calm in contrast.
Hanoi is fine
The scooter traffic is mad, but it’s a lovely city.
Also thought hanoi was fine
I think the sheer volume of motorcycles and the difficulty of crossing the street can be very overwhelming for people.
Was going to say Hanoi. I don’t know why people characterise it as this tranquil quaint little place - it was madness when I visited.
Hanoi is chill comparing to HCMC .