Except things like 26/11 or cricket, Pakistan is never brought up in conversations among south Indians. The only things south Indians and north Indians have in common is nationality. It's a completely different culture, like someone else pointed out.

There's a lot of interesting social dynamics because of this. Most north Indians struggle to communicate in the south because while Hindi is universally taught all across India, southern languages are only limited to the south. So as you can guess, south Indians in general don't have much of an issue living in the north (although there are exceptions).

What's even weirder is there are four different main languages spoken in the south too, so there are internal differences among south Indians as well.

All in all, if you are in a big city anywhere in India you should be able to get by with English and basic Hindi. But go anywhere beyond and you will struggle if you don't know the regional language and don't have a local friend with you. I guess this applies anywhere in the world, but I find it really weird that it happens to people of the same country.