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?
I’ll throw in some cities that haven’t been mentioned:
Tehran - Similar to Cairo where traffic rules are a “suggestion” and makes Cairo seem orderly by comparison
Rio de Janeiro - Parts of Rio can be overwhelming and unsafe, especially if you don’t know what you’re doing. Even more so with Salvador
The Tenderloin area of San Francisco - Especially with the wealth inequality and multi-billion dollar tech offices and HQs literally around the corner.