I think I'd die hearing or seeing my parents doing 'it'. You're right Sister- my parents have only done it to reproduce and accidentally- I'm certain they hated it and barely touched!!!
My kids are at an age where I can pause- DD4 walked in whilst I was flopping around on her Mummy... I just moved very slowly towards my underwear as if DD4 was a tiger. She started talking about a nightmare she'd had about some witch turning her into an apple- it was fine "mummy where's your pyjies?" - "I was hot". Phew!