Breakdown of Tu te comportes comme si tu étais le marquis !
être
to be
tu
you (informal singular)
le
him, it (masculine direct object pronoun)
se comporter
to behave
Questions & Answers about Tu te comportes comme si tu étais le marquis !
Why use the past tense étais when the behavior is happening right now?
What if the unreal comparison was about something in the past, like "You behaved as if you had been the marquis"?
Why is there a te in tu te comportes?
The verb for "to behave" is the reflexive verb se comporter. In French, you literally say that you behave yourself, which is why you need the reflexive pronoun te matching the subject tu.