I'm not sure I like 'yeah'. It seems a bit dismissive, as does the now-universal 'whatever'.
I recently joined Facebook in order to leave a message for a chap who has my maiden name and lives where my father was born. He's called Duncan. My message was very polite, and gave a few details of my grandparents, as I suspected the man is actually my cousin.
I received a reply which said,"Yeah. Your dad and mine were brothers. So yeah, we're cousins." I must be a ghastly snob, as I didn't like the sound of him at all.
My funny sis later told me she already knew of Duncan. It's true he is our cousin and he's a terrible racist, member of the BNP etc. She double-dared me to send him a photo of my husband, but I haven't yet!
He'd be horrified innit? Yeah!