It's a rare find: an iPhone app that's both useful and hilarious. RunPee, an existing website that launched its iPhone app today, checks both those boxes.

Here's the idea: you're watching a movie in the theater and need to take a restroom break, but you don't want to miss the best part. The RunPee iPhone app has a timer letting you know when it's safe to take a break, and gives you a summary of what you missed upon your return.

It also lets you know whether you should stay till the end of the credits, since movies like Iron Man include bonus footage afterwards. You start the timer when the movie begins, and safe break-times are scheduled throughout. The app costs $0.99 [iTunes link].

In an amusing press release for the iPhone app, creator Dan Florio explains: