Well now, that depends on a number of things doesnt it? First of all I'm assuming your question is a typo of some sort and you meant "sister- IN- LAW" and NOT just your sister. If you are 13 or younger you're probably going to have a tough time no matter what the case may be--What makes you think she wants to sleep with YOU kid? If you are OVER 13 and married are you referring to your wifes sister? Is that the REAL reason you married her? Just for a shot at her sister? Yikes! I feel sorry for your wife man! It just occurred to me that I might be wasting my time even trying to be funny here because, if this question is NOT yanked by the mods, then wouldn't that be a knee slapper?