Pakistani’s are almost always Muslim (due to Partition [https://en.m.wikipedia.org/wiki/Partition_of_India]), and will often act and speak differently in several telltale ways for anyone who knows what to look for. Both given and family/surnames are also often telltales.

And if you think Casteism is a bitch, Pakistani/Indian (or Indian Hindu vs Indian Muslim) is a bitch and a half. Just try to apply for a visa for India and see how many times they ask if you or any of your relatives are from Pakistan to get a taste.

Edit: ooh, downvotes away. Hah! No better way to tell when you hit a nerve than the torches come out.