cool as a cucumber
calm and relaxedContext:
Friend 1: Herbert and I witnessed a pretty bad car accident yesterday.
Friend 2: And of course, Herbert jumped in to help, right?
Friend 1: Yes he did. People were crying and bleeding and it was total pandemonium but Herbert remained calm, took control of the situation and probably saved some lives with his clear thinking.
Friend 2: That's Herbert. Always as cool as a cucumber.