A White Boxer

You pulled down your jeans.

"Alex, are you wearing a white boxer?"

"Yeah, how do you know, the dress is black."

"Your boxer is so big that it can be seen underneath the hem of the dress!" Alison laughed.

"But guys wear boxer!" You retorted.

"Not when you're wearing a dress, silly. Here, try this."

She tossed you a black piece of fabric.