I have a jade bracelet with the band made out of string, and it's done up in such a way that you can take it on and off; there's this nifty little thingy that lets you tighten and loosen the band. Granted, you still kind of need two hands (or your free hand and your teeth) to do it, but it can be done.

We also had friendship bracelets, which operated on that premise--that they only way they come off is being cut off or broken. You and a friend would make one and swap them.

*snickers sophomorically at the thought of John and Rodney exchanging friendship bracelets*