I’ll post a poll on this.
I’m on a business trip. I change my underwear everyday and I don’t have a unworn pair for tomorrow which is my return travel day. Do I:
Rinse a pair out in the bathroom sink, hang them to dry in the shower. If they aren’t dry by morning, use the blow dryer to finish drying them.
Wear a pair that you wore earlier in the week, preferably the cleanest you have. Do take a shower before getting on the plane.
I was going to say wear a swimsuit under your pants, but then I saw you were on a business trip, so I’m guessing you didn’t bring a swimsuit with you.
I take it your hotel doesn’t have a laundry service or coin op laundry, or it isn’t feasible to use it and get your clothes back in time for your trip. If they did you probably wouldn’t be asking.
So I concur with the above (ETA: two posts above now – kenobi 65’s post) post. Wash a pair in the bathroom sink and hang them up to dry overnight. You can even wash them with the bathroom soap if you want to do more than just rinse them. Hang them in front of the heater vent to dry them faster, if possible. If not possible, do what kenobi said.
This, the 4th option that wasn’t in the poll.
I always just buy some more.
Hell yeah, that’s why the internet is great. I’ll wash a pair in the sink.
It’s late, I’m about to go to bed, my co-worker is the rental car driver and I don’t have cash on me for the hotel’s laundry (and I don’t feel like waiting up on it). Sink washing it is!
Do take the shower as well.
The hotel shampoo usually works great for this. Stretch them out on a hangar to dry. If they are hanging down in folds they’ll still have streaks of damp in the morning.
Been there, done that, blow dried the t-shirt. 
Shower is a given, I live in a society.
Fail safe drying: hang them over the heater blower.
(Not on the heater)
What’s the issue that you are trying to resolve?
Is the underwear soiled beyond recognition? Then rinse them out.
Or simply worn-for-a-day? Then flip them inside-out so you have a clean-er surface touching your skin.
I would probably go commando if I still have a full work day ahead of me before traveling home. If I was going right to the airport to go home in the morning, I’d probably re-wear the ones I currently have on.
My rule of thumb on business travel packing:
One pair of socks for each morning I’ll be gone +1
One pair of underwear for each morning +1
One pair of undershirts for each morning +1
And always travel with more than just the pants you’re wearing, even for overnight trips. Always pack an extra. If you split the pants you’re wearing, it’s kinda hard to run out and buy another pair. I learned this the hard way.
Go commando.
And learn the difference between “ran” and “run”.
As others said. Wash in the sink night before you are going to leave. Wring them fiercely. Hang them to dry. Blow-dry before hanging (post wringing) and once again in the morning.
Seriously, I thought this was standard knowledge?
I know the difference. It’s “ran”… as in, “I’ve ran out of underwear”.
After you wash the underwear, roll it up in a towel. Stand on the towel to press all the water out of the underwear and into the towel. Unroll. The underwear will be drier than if you’d wrung it, and it won’t be all stretched out.
No…if you’re going to stick “have” in the sentence, it’s run.
Anyway, the real answer is none of the above. Either rinse a pair out or buy another.
nm