I don't know if you'd call it a dare, but here's something I do semi often: hold it for 24 hours.
That's it. It's that simple. Or is it?
The concept of the dare is that you must stay in diapers for 24h without ever using them. My favorite way of doing this is as follows:
-Go to the bathroom at around 9-10pm. Make use of that bathroom trip. Once you're done, proceed to a shower. Make sure to take care of your privates, both in terms of washing and drying them, as you're about to trap them and forbid them access to air;
-Pick a nice diaper and put it on. Simple enough. Whatever you do for the next 24h, keep that diaper on. No exceptions.
There you go! It's quite simple, but the fun lies in that once you hold it for 24h, you get to let everything go in your diaper. You'll end up with one of the most relieving wettings (and eventually messes if you're into that, I sure am) you've ever experienced.
Have fun