Fake-an-Excuse does exactly what it sounds like. During your iPhone conversation, hit the home button, fire up this one-dollar iPhone app, then dial up an appropriate sound clip. One example: "I'm being pulled over (siren)." The person on the other end of the line will be fooled and will quickly end the conversation, allowing you to get on with your life.
One problem with this scenario, though, is that all of the excuse-based audio choices are muffled and tinny, which makes them fake sounding. I don't know if the bitrate of each audio sample had to be small to cram into Apple's 10mb app file size limit, but perhaps dumping several of the more useless excuses (good for a laugh, but not really for an excuse) and improving the audio quality of the remaining samples might have been wise. Will anyone really be fooled by the sound of swarming bees or an explosion?
Still, Fake-an-Excuse is a silly utility that frequent excuse seekers might actually find some use out of. And it's only a buck, which buys more than a dollar's worth of entertainment, even if that's ultimately all you get out of it.