There is no need to feel ashamed of yourself in this life. If you are feeling ashamed of yourself or anyone else that is not a life. If you are ashamed of yourself for whatever reason, you can't live. I know girls that are ashamed of themselves 'because they're not pretty enough' or 'they do things to themselves that are considered inappropriate'. Of course, those aren't all the reasons you can be ashamed of yourself but the ones I have experience with. Who says you aren't pretty enough? I know that the pictures we're surrounded by every day and our culture defines perfection as everything we're not, or something we may have a piece of, but not enough of. Perfection is defined as: the state or quality of being perfect: a person or thing considered to be perfect or the action/process of improving something until it is faultless.
It's unfair to measure yourself by this defintion. Because everybody is different. Perfection would be no fun. It is unachievible though. Anyone can find a fault in anything - so expecting perfection is unrealistic. Don't be ashamed when you don't measure up to perfection - although society nowadays craves it - no one can be, you don't know what those models or celebs who appear to be perfect do when the camera shuts off or behind closed doors. They are just normal people. Things go wrong in their lives just as much as in ours but they have learnt how to channel it into what they do - or they just don't announce it to the public and deal with it privately.
If you're ashamed of 'doing something that isn't considered appropriate' it's your mind you need to convince that it is ok. Nobody else has the right to be disappointed in you or make you feel ashamed of yourself. If you're regretting something that you have done, it's your mind that is your enemy. And it is not easy to convince it otherwise, it does take time unfortunately. But hopefully you can turn the volume down on that voice in your head that is criticizing you. I have personally gone through this - so I know it's not an easy battle to start or complete but it is possible.
Probably just me rambling again, but honestly if you do feel ashamed of yourself for 'not being pretty enough' or something, there is really no need for you to be. Get your head out of the magazines or whatever it is that is telling you you're not good enough, look in the mirror and say. 'This is me, this is who I am, and even if I don't know yet, that's Ok.' You are constantly growing, constantly changing so don't be held back by yesterday's actions because that's the past, there's nothing you can do about it now. Hope this has helped,