While they are in the house?
Following on from the vibrator thread my instant reaction was no, I wouldn't take a vibrator to my parents house and use it. But then, how different is that to having sex at your parents house? I know I had sex at my parents house when I was younger (I lived with my Mum till I was about 24 so it would have seriously cut down on my action?) although funnily enough I don't think I would have sex there now.