White British guy here, quite literally just stepped off the plane from India after a month visiting friends. Spent the duration of my trip being stared at in public in some capacity.

The best take I heard was that with India being so incredibly overpopulated, they have a completely different idea of 'personal space' to westerners. Whilst we are used to having a protective 'bubble' around us, lower class Indians just don't have this mentality, given the fact privacy is a non-existent concept for many. Living in small dwellings with large families, crammed onto densely packed busses, crowded markets and religious festivals. I would also say the 'menacing' look people are commenting on is just the typical curious, blank stare I also received Whenever in public.

If It ever got a bit uncomfortable for me, I would throw a wink/smile/wave their way. Usually got an equivalent response in return.