"I'm just meeting with you [the recruiter] -- it's not like this is a real interview."

While recruiters are not the ultimate decision maker, they do make the decision on whether or not to present you to their client in the first place. In your interview with the recruiter you want to dress and behave as you would for a company for which you want to work.

You can be more open with the recruiter as to your preferences, but when it comes to professionalism, bring your A-game.