customer

an awkward customer

a person, group, or thing that causes problems, usually because they will not behave in the way you want or expect them to. There's usually at least one awkward customer who insists on doing everything according to the rule book.

a cool customer (informal)

someone who stays calm and does not show their emotions, even in a difficult situation. I can imagine Pete being good at negotiating. He's a pretty cool customer.

See also: cool