Eu tenho uma resposta em Como Bruce Banner se tornou o Hulk à vontade? , que responde como ele é capaz de manter sua inteligência quando ele é o Hulk. Em suma, a partir do filme anterior Incredible Hulk (2008), ele treinou-se para que pudesse transformar-se voluntariamente no Hulk, e, como se vê, manter o controle.
Quanto ao que Bruce diz:
I don't believe he literally meant that he is angry all the time. It was said in jest or more likely a catchphrase before punching and bringing down an entire enemy ship.
Quanto a como é incapaz de manter sua inteligência, eu a atribuo a
Loki's staff that was in Bruce Banner's vicinity on the Hellicarrier (ship). I believe Loki's intention of being captured by S.H.I.E.L.D. was to get the staff near Dr. Banner to induce everyone near it to become angry and hostile towards one another. Couple that with the ship being attacked, Bruce would then involuntarily turn into the Hulk, which he would have no control over.