I'm looking for a word/phrase meaning a person not getting worried or not hurrying in situations where most people do and get butterflies.
For example, you want to go on a trip by train. You've got your tickets and there is 15 minutes left to catch your train. Your husband or wife doesn't seem worried at all and keep saying "there is no rush." And you're all like are you kidding me?! and you say
How can you be so relaxed?! You're such a [the word/phrase]!
Or you have a test and you need to study but you all seem so casual like you have all the time in the world. Your mum sees you and says
You're really a [the word/phrase]! I'd study harder if I were you!
As you see this is what normally people get suprised by so I need a word with a negative connotation. Adjectives are also OK.