Tell them to blame you. My mum told me this trick and it worked a charm. Whenever I was invited somewhere that I didn't want to do or to do soemthing that I didn't want to do, I would balme my mum. 'No, if my mum ever found out I would loose my car' or some such. Yes, they might get labeled a mum's boy by the 'cool kids' but, in my experience, a lot of kids were very sympathic and would start to talk to me about it 'Wow, your mum is reall strict! what else can't you do?' and the topic was completely derailed