In his youth, he strongly reacted against his parents' conservative values.

reacted 是动词 react 的过去式，react 由前缀 re-（表示"回、再"）和 act（行动）组成，本义是"作出反应、回应"。 against 是介词，表示"反对、对抗"的意思。 reacted against 这个短语表示"对...作出反抗/反对的反应"，强调对某种观念或行为的抵制态度。