Polo shirts included. Wearing a t-shirt under a polo or button down is insane. Almost as insane as calling button downs, button ups. Children wear t-shirts under their shirts. Do you still wear long sleeve t-shirts under your t-shirts? Still have a bowl cut? If you answer no to those, then you’re far too old to be wearing a t-shirt under your polo and button down. The only time it’s acceptable is if you’re also wearing a tie and you’re a big sweat guy.