Flakiness is sooooo annoying!

It's such a simple situation, if you say you're going to do something, then do it! If not, then don't say you will in the first place. Especially if you don't even have the courtesy to let the other person know that you've changed your mind for whatever reason. If you do have a good reason, then obviously it can be forgiven. But even if you don't have a good reason, it's always best to let the other person know what's going on. Instead of leaving the person hanging, wondering what's happening. Golden rule people, treat others how you want to be treated.