No one is having fun in this interview. If this is indicative of the kind of interview Cara is going to give American's she can wave a premature bye bye to her future movie career. It's not that they don't get sarcasm, they just don't appreciate it, which is an entirely different matter altogether.
Perhaps Cara is making the age old mistake of overcompensating for any nerves/underlying hangover (the premiere was the previous night) with brute nonchalance. But - to be fair - I don't think she comes across as "irritated." Much.
It hasn't been the best of weeks for Cara (relatively) as Kate Moss has reportedly 'blacklisted' her. A random source speaking with The Sun said: "Kate has blacklisted Cara now. It’s very unfortunate and hopefully might be a temporary thing, but they’re definitely not friends at the moment. Kate wasn’t happy with Cara’s clash with Naomi and felt she should have treated her with more respect. Kate is also unhappy with Cara about ditching Storm. Kate has remained loyal to Storm throughout her career and thought Cara should, too".