Going back to the original comment- I was making it clear that nobody needs to pat someone on the back to figure out if they are brahmins - you can tell from the last names.
I dont really know the castes of my friends except Brahmins, because they keep informing me.
1. Tamil brahmins - any domestic post on Facebook has a reference to the "TamBram" community.
2. My manager informed me once that the reason he was light skinned while south Indian was because his ancestors were north Indian brahmins who moved to the south to work as priests. I never asked him about his skin color. He brought it up himself.
3. One of my peers - a maharashtrian brahmin explained to me how his particular brahmin subcaste was even superior to other brahmins because of some XYZ reason. I didn't know he was a Brahmin before this.
There are several more instances. Of course, there must be brahmins amongst my friends where I don't know about their caste. But the only friends who have brought up their caste voluntarily were brahmins.