Can you say "Unlike his friend, he still looked agitatingly calm"?

I've read the word agitatingly before too... so that probably is the right spelling. If you still want to rephrase, then here are some suggestions: " To his friend's annoyance,he still looked completely calm" or " It was irritating(or irritated) to his friend that after everything, he still looked so calm". Although I don't know if the second one will work for your story or not.