Whenever I tell someone I'm an app developer, they invariably have some great app idea they insist on telling me (even when I say "Don't tell me your app idea"), and then they say if I ever use that idea remember to pay them.
Now, I already have my own long list of my own varyingly vague and obvious ideas, which I'm putting down here, so, again, don't tell me your app idea, but if you do, it's going in this list that I will probably never get around to, and even if I do, if you can do a better job implementing it, go for it (just remember to pay me, ha ha).