When I have a girl round my place, I love to massage her bum during foreplay as it turns me on greatly (the butt's my favourite part of a woman) and the girl usually seems to like it too. However, so far I've just been using my bare hands to massage, rub and knead girls' bums. What's the best oil or cream I can buy that will provide lubrication and make the massage more sensual and enjoyable for both parties?