I think most of us thought Cilan never cared when Iris called him "a pain" regarding his antics, until we realized all those times Iris has said it she was basically talking to herself. It was directed to Cilan but not at Cilan, this episode's the first time Iris has directed that comment right at Cilan. Guess having someone else who thinks exactly the same with Cilan's oddness as Iris (Dawn) is what caused her to directly speak out her thoughts.
From this (and a few other times it's happened) I realized Burgundy's the only person who's insults and harsh comments are unable to get to Cilan.
I found Dawn's sarcastic remarks towards Cilan's weirdness funnier than Iris groaning about him being a pain at the back. And from this I loved that Iris yells it at him because that's the first time Iris had a different reaction. Cilan was adorable when he started sulking and also when he recovered.
People who think it's unbelievable for Cameron to be strong because he is kind of an idiot clearly haven't been viewing anime properly.
Anime has proven that characters don't always have to be geniuses to win in a battle, for some people brawns is what works for them.