Thanks quietlyspoken08 it is indeed the glimpses of their "true" selves that keep you going through the dark days... rarely glimpsed but usually emerge on family occasions where extended family is present, or when teen has just achieved something they are proud of, or brings home new gf or bf 
Also I just wanted to say to Raaarrrrrrrr that I so agree it can be very lonely as the parent of a teen sometimes. Friends refer to teenage angst in passing, but somehow it is not as socially acceptable to discuss difficult teen behaviour, as it is to say you are finding it hard going with a baby or toddler.
I'm not quite sure why that is; I think protecting the confidentiality of a now nearly adult child has something to do with it, also maybe people feel themselves that they should have a handle on the parenting lark by now and feel embarrassed (which they shouldn't do because this is a whole new different stage requiring new and different parenting skills). Also, there are more social situations where mothers of toddlers and infants naturally gather together, either at baby groups or around the nursery school gate, but of course as the parent of a teen you may not be doing the school run any more or mixing with other parents at extra curricular activities, except to drive them there occasionally and then you are under strict instructions to hide around the corner
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So being the parent of a teen who is acting up, can be very isolating and distressing if they are challenging you a lot, (a) because the small person who you used to play with and hug and who came to sit on your knee, has now done a nearly complete 360° and is challenging everything about you; your authority, opinions, principles, methods! And it is quite shocking when you feel you personally are being targeted and by someone you love so much. And (b) teens can be physically large and it can even feel intimidating occasionally and they have all the time in the world to argue a point if you let them. One of mine can argue the hind leg off a donkey given the chance but I know the signs now - it is usually when she is feeling badly about herself - and I walk away until she simmers down enough to come and tell me what is really wrong, as a minor dispute can deteriorate quickly in to a major argument otherwise.
Sorry for essay but I don't think there are enough opportunities for parents of teens to meet and discuss these things.