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?
Damn, that metro sticks in my mind. Mostly for one reason.
You know that “protocol” where people boarding should let people off first?
Well, on a scale of 1 (impatient ) to 10 (Japan level politeness) NYC scores about 6 and Delhi scores -100 (minus 100).
To exit at a busy station, I had to really put my shoulder into it and channel “the refrigerator” William Perry.