catch sb. on the hop 使某人措手不及
A: It's a great pity he left suddenly.
B: Yeah, He caught us on the hop.
A: He has lost a good chance to understand others.
B: Perhaps you're right.
chat up with 与……搭讪上
A: Henry is chatting up with the pretty girl.
B: He's always popular among girls.
A: Perhaps because he's very handsome.
B: Not exactly. I guess it's what some people call"charisma".