Cas - despite anxiety or shyness, returned the handshake. Of course, he's not very good at social cues and so it probably goes on for far longer than is strictly necessary.
"It's alright," he amends once they all have their hands back to themselves. "I'm Cas. I don't know John exceptionally well. He's more friends with Dean." At that, he turned around zoning in on his husband and pointing. Of course he could find Dean in a crowd without effort. "He seems nice, though."