If you’ve been hooking up for a while, especially if you live in a small town, eventually you’re going to run out of women. Or perhaps you’ve always had a fascination with your friend’s sister, and you’ve always wanted to try out a little something with her on the side. We’re not going to tell you not to go for it, because we’re also men in the need and we know how difficult it is to ignore those urges. However, there are some ways to take what could be a potentially disastrous occasion and turn it into something fun and easy.

DO: Ask If It’s OK First

“Ask her – if she is ready”

We’re not saying you need to ask your friend’s permission to sleep with his or her sister. What you need to do is sound out whether, hypothetically, he’d be all right with someone sleeping with his sister. This isn’t the 1700s, and you don’t need permission to get between her legs. Just make sure that you’re not going to treat her like a creep, or that your friendship with this bloke isn’t going to be over when he finds out. Of course, if his friendship isn’t that important to you, go ahead and do what you will.

DON’T: Tell Him About It

If the truth comes out, the truth comes out. That doesn’t mean you want to rub it in your friend’s face. Don’t bother hiding it from him, and tell him what happened if he asks. However, he’s not going to want to hear the details. Don’t tell him about “some bird” you hooked up with last night, only for him to later find out it was his sister. Just assume that the truth will come out at some point, and proceed accordingly. You don’t want it to turn into a storm of drama when that could have been easily avoided.

DO: Enjoy Yourself

“Take advantage of the situation once she is ready”

You won’t have many opportunities to enjoy something as forbidden as your friend’s sister, so make sure you’re going to make the most of this chance. Live it up, and make sure she’s enjoying herself as well. If she wants to make it a regular or semi-regular thing, consider your options carefully—but there should be no reason you can’t have your friendship and eat her too. You’re not doing anything wrong, so enjoy the situation.

DON’T: Act Like a Boyfriend If You’re Not

If you’re not planning to date this girl, do NOT act like you’re going to be her boyfriend. Dating or shagging your friend’s sister is one thing. Breaking her heart and acting like a predator is a complete other thing, and you don’t want to see the other side of most of your friends when their sisters are preyed upon by someone they know is unscrupulous (let’s face facts). If you don’t want to hook up with her anymore, tell her plainly. If you do want to, let her know that you’re not looking for a girlfriend. Be more honest with her than with other girls.