Well, if she was going to try to make him jealous--which he was--and call him sarcastic to boot, maybe he'd just live up to that.
"Jeremy. Well, it's nice to meet you. I've heard all about you." Lies, lies and sarcasm. Made clear by the fact that John gripped his hand a bit too hard during the handshake.
John already hated him, and Jeremy was well on the way to not thinking well of him.