Severus tried to look around to spot the boy that was making Lily so nervous but he couldn't really see the Potter-ish looking boy well. Of course it was hard to follow and listen to Lily while looking back.
"Do you want me to go talk to him?" Would he glare at the boy and tell him to keep his eyes of Severus' girlfriend? He would love to do that but that would probably embarrass Lily and that he did not want to do.