[PurveyorOfFineDares]

Here you go! I can't take full credit for this one, it was inspired by something similar I saw on here before.

Materials:
Six envelopes
A backpack lock and key
Six nude pictures of yourself (can be faceless if you find it too uncomfortable otherwise)

Preparations:

Fold the key inside a blank piece of paper and put the paper in an envelope.
Fold a fake key inside a nude picture of yourself and put the picture in an envelope (use a coin, maybe, you just need to not be able to tell the envelopes apart by weight or anything). If you want to do this without buying a lock, just write “key” or “not key” on bits of paper and trust yourself to be honest, but I think this works a lot better if you’re really stuck until you find the right envelope.
Choose which campus you’ll do the dare at. If you choose the big one, repeat until you have four envelopes with nudes and one with the key. If you choose the small one, you need six nude envelopes and one key envelope. You should not be able to tell the envelopes apart once they’re sealed.

Go to campus. Choose a home base near the middle of the campus where you’ll be able to hide your backpack later.
Leave an envelope in each of the following places if you’re at the small campus. Only the first five if you’re at the big campus. Make sure at least three of the envelopes end up in completely different directions from your home base. Tape them in place if they might get blown away.

At the very edge of campus, as far as possible from your home base.
By a large sign with the university’s name on it
In a random window of a male dormitory
The entrance of a building you have a class in
Set a timer for 10 minutes. When it goes off, you have ten seconds to place an envelope somewhere nearby.
Set a timer for 5 minutes. When it goes off, you have five seconds to place an envelope somewhere nearby.
Under a lightpost, fully illuminated.

The dare: Start it very early in the morning, aim to time it so that you’ll have to hurry to find the envelopes before the sun comes up and people start arriving. Strip completely naked at home base and put your clothes in the backpack. Lock the backpack and hide it. You may now collect the envelopes in whatever order you like, with or without returning to home base after each one. However, you may NOT open any envelope until you are back at home base. If you open an envelope and it has the key in it, but there are still envelopes you haven’t found, you have a choice: You can open your backpack and get dressed, ending the dare, or you can stay naked and get the other envelopes. Of course, if you end the dare, you must never retrieve your other pictures!