Denim girl,
Listen to popa.
His joke really explains best of all the reason it’s not appropriate.
First impressions are lasting impressions.
Think about it. Would you want a guy bringing you to their yeshiva dining room for your first date (apart from the onlookers)?
How about your date showing up grungy after a long day? Even if he straightens out his clothing, he just isn’t his best.
Men are very visual. The efforts you make to look nice show how much you value your date. You might think a jean skirt looks nice, but many men wil not look at this as a flattering look. Think about it this way: casual look, casual interest.