The underwear.

"I choose the briefs!" You quickly say.

"A predictable choice." Ms. Vickey said as she slid your new uniform across the table. "But a good choice none the less..."

In a quick swipe of her arm all the other options disappeared into the older woman's hands.

"I'll be right back, and when I return I expect you to be in your new uniform. Understand?"

"Y-Yes ma'am." You stutter as you hold up the small scrap of cloth. "Actually this is a bit small. Do you have-"

The door slammed shut as your principle's heels clacked away at the tiled floor of the school outside the office.

"Maybe she didn't hear me..."

You decide that you'll just have to bring it up when she gets back. Perhaps she doesn't care what type of underwear you choose. There are quite a few brands that offer more swim trunk styled boxers that would be preferable to this.
Or maybe the briefs aren't that bad. It's possible you're just psyching yourself out, building up nerves over nothing.

'Well there's only one way to find out' You think to yourself as you strip out of your current clothing. Darting your eyes around the room you shuffled out of view from the clear glass door. No one was passing by and the office seemed devoid of security cameras.

In a quick blur of motion you hooked your thumbs into your boxers and pulled them to your knees. Less than a second later the briefs replaced them.

Your worst fears about your new 'uniform' where confirmed. The white briefs where tight, very tight, even tighter than you imagined. The front was so tight that the small slit in the front was ever so slightly open. You felt a small tickle of air against your shaft that pressed snuggly up against the forward opening. There's no doubt in your mind that even a semi-erection would burst through the gates.

Moving to the mirror on the opposite side of the wall you find the first thing that's immediately and unignorably noticeable is the large bulge you're now sporting. It thrust forward lewdly as your underwear is tight enough for the outline of your member to be very defined, and this effect wasn't unique to your penis.
Everything from the crease of your hips to the dimples of your ass is clearly outlined through the skin tight material.

"Very nice Mr. Doe." Ms. Vickey said as she re-entered her office. "I think the uniform is a great fit."

"Well I don't! It's so tight that it might as well be painted on! You have to have a size or two bigger."

"I see. They do seem to fit your form very well. I'm sure your peers will have trouble keeping their eyes off you. I know I am." The brunette snickered. Her eyes not seeming to move north of your waistband as she spoke. "Because of that I feel they are the perfect size for this punishment."

"What?! H-How?"

Moving to her desk Ms. Vickey shuffled through the stack of papers she'd previously plopped down. Clearing her throat she read one of them aloud.

"Anonymous staff complaint: Dear Ms. Vickey. I regret to inform you that I've caught one of my students, John Doe, staring down my blouse on multiple occasions during class. Please discipline him as I feel it is both affecting his grade and my temper."

"That's not-"

Ms. Vickey gave you a quick hush before shuffling to a new paper.

"Staff complaint from the physical education division: Ms. Vickey I must report that the student John Doe seems more interested in observing his fellow student's attire, specifically the back of their shorts and the front of their shirts, than focus on his own physical education. I request that you correct this worrying behavior immediately."

"There are quite a few of these reports Mr. Doe, and that is exactly why I feel these are the perfect size for you. Maybe learning how it feels to be ogled by the opposite gender will prove to be a valuable lesson to you. For your sake I hope it does, because If I get one more report of perverted behavior I'll do far more than simply strip you naked."

"This is insane!" You say as you march towards Ms. Vickey's desk. "You, you can't honestly think this punishment-"

As you moved forward your steps became a bit too aggressive. The bouncing caused by your movement allowed your dick to spring free of it's fabric prison and perfectly present itself at eye level to the seated principle in front of you.

"Pfft! Oh my Mr. Doe, you should be more careful with your new uniform."

"What? What are you..." You began, confused at the odd sight of your principle breaking her cold attitude to **** back a laugh. With a quick glance down you instantly recognize the problem and scramble to cover yourself.

Clearly trying to hold back more laughter, Ms. Vickey spoke as you stumbled around with the opening to your briefs. "Now then your English class has already started. I'll give you five minutes to get there before I count you tardy. It would be a real shame for you to loose your uniform one day into getting it."

You stare back at your principle. Unsure whether to take your chances arguing more or to rush back to Ms. White for the most humiliating presentation of your life. Something tells you that if Ms. Vickey is willing to go as far as laughing at your wardroom malfunction, that she probably isn't lying about her threats to strip you nude.

Giving her a mean glare you turn heel and move your bare feet from the carpet of her office to the tiled floor of your school.