if you describe the way someone treats you as a kick in the teeth, you mean that they treat you badly and unfairly, especially at a time when you need their support. She was refused promotion which was a real kick in the teeth after all the extra work she'd done.

kick yourself, if you say that you'll kick yourself when or if something happens, you mean that you will feel angry with yourself because you have done something stupid or missed an opportunity. You'll kick yourself when I tell you who came in just after you left. If I don't get one now and they've sold out by next week, I'll kick myself.