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?
Medellin could be overwhelming at times, particularly if you travel there solo. Wouldn’t dream of driving there (crossing the street was enough of a challenge), constantly having to watch your back for thieves, and noisy around certain districts in and near the center of the city.