DD is 10 (but likes to think she is older) and I let her have a sleepover last night with her friend. While her friend was here she took a box of mince pies from the kitchen without asking (I found them when I went in to her room for something else), took an entire box of Roses and denied it when I asked her and was generally pushing me to get me to react, answering back and being disrespectful.
I'm not a total soft touch though I hate shouting and have had to crack down on her behaviour in the past, we have had issues with lying and even stealing on one occasion. (I rumbled her and took her back to the shop to be bollocked as well as punishing her myself). It has been generally better over the last year or so, since we moved house and I had my DS, who's now 8 mths. We moved for 6 months then moved back and over the last few months she has got gradually worse again. She tries to show off in front of her friends and is far cheekier as I don't tend to like to make a show in front of them. She has also broken two beds over the last year and lost an ipod and seems to have no respect for hers or others property either.
Her dad, my ex-h was abusive towards me and I left him when she was 5. She saw him assault me when she was 3 and she still remembers this. After I left he was convicted of assaulting me and we have had no direct dealings since as he was an arse every time I saw him, so his parents drop her off and pick her up when it's his weekend. She sees him every other wknd and goes for tea once a week.
He is a compulsive liar and has no respect for his parents, who bend over backwards to try to help him. He has never paid me a penny in maintenance for her but she thinks the sun shines out of his arse. He never tells her off (he doesn't need to) and whenever she goes to his or his parents she gets spoiled rotten.
Sorry for long ramble, didn't want to drip feed.
So, when her friend left I asked her again about the missing chocolates and she kept lying to me, then picked up her laptop from where it was in front of me and walked off while I was talking! So I grabbed the laptop, and took it off her and then she hit me on the arm. 
I was furious, stormed upstairs and took her tv, 3ds etc and brought them downstairs. I didn't shout but I told her to stay in her bedroom and that I was going to calm down downstairs then we were going to have a serious chat. I've got a poorly baby atm as well, so the next thing was when I heard the front door slam. I went straight after her but she had gone and I couldn't leave him to go after her.
To cut a long story short, I then had a call from her GP's to say she had phoned her Dad and he was on his way to pick her up and they were going to take her back to their house. I spoke to her GD who told me that she had been cheeky to him over Xmas but that he had told her off too, but that they admitted she tended to get her own way a lot when she was with them. She seems to have little respect for her nan in particular, which I think it to do with how her Dad talks about her. They then brought her back after giving her tea. When she got back she was still defiant and had obviously had lots of attention from them and tbh was scarily unrepentant.
I was at first angry and shouted, but that didn't affect her at all and she shouted back, so then I told her she was grounded for a week, losing her privileges until I decide otherwise and that every time she answered back I would add on a day. I think then she knew I meant business so then I was really tough with her and was as hard faced as I could be. I was so upset that she could lash out like that and also that she put herself at risk by running off.
It seemed like it had gone in and she did as she was told when I told her to get ready for bed, but then I heard her singing to herself! Like she had not a care in the world. AIBU to be the biggest hard ass in the world now and over the coming weeks/months/years? I'm worried as she has respect for the men in her life, (her Dad, GD and my DH) but not the women, (me and her GM) and I'll be buggered if I'm letting her continue with THAT attitude.
I'm stuck with Bad Cop for the foreseeable aren't I? Shit I hate being Bad Cop. :(