[dorp0]

Without leaving the room, get your underwear that you have worn all day off your body. How you do so is up to you, but you may not leave the room. Then just casually drape them over your shoulder like a chef's towel and hang out like normal. Make it obvious it isn't a real towel. Have a snack and occasionally wipe your fingers or even your mouth on them, so you stay neat and clean.

Might as well open the curtains and let in some good light. Pick a busier time in the afternoon/evening. Try to leave them on your shoulder for at least an hour.

Edit - Bonus points if you go shirtless or at least wear a muscle shirt open/ripped down the sides.
Edit 2 - I would think hiding under a blanket or similar to get off the underwear would be taking the easy way out, but I did say it was up to you.