Explain how you’re not actually related without freaking her out: Pretend like you're trying to casually start a conversation. "So, Jessica, how are we related?" Eventually, you will work her to the conclusion that, in fact, you are actually not related at all.
This is an Untapped Resource to keep on the back burner, just to cover your bases. We've all been at family parties, bored out of minds, watching our Dad's get drunk and our sisters get eye-banged by our creepy uncles. Well now I've got something for you to do at these family functions: Your increasingly beautiful cousin who is not actually related to you by blood. We all have them; they're our mother's sister's husband's sister's daughters. Or something similar. Here's what to do.
Reminisce: "Oh man, do you remember when we were kids and we used to catch tadpoles in the pond by your house? That was the best! We used to be so close. What happened to that, I always really liked spending time with you." That last statement begins the wooing process. Finish with, "I miss you."
Turn a hug into a snug: Give her a playful cousin hug, but turn it into something more by following these rules. 1) Sigh deeply as you tighten your squeeze just a little bit. 2) Hold the hug three seconds longer than a standard hug. 3) Grab her left breast as you come out of the hug. Now that's snugging.
Sneak off: After the snug your not-really-your-cousin will totally follow you anywhere. Try going to the room upstairs where everyone put their jackets. The extra padding on the bed not only allows for very sensuous love making, but it provides all kinds of shadowy nooks for you to cloak your sinful ways.
Make that sweet, sweet love: Don't worry, she's not your blood cousin. Still, don't tell anyone about this. They won't understand. And remember to cuddle for a while, basking in the warm afterglow of amazing sex. As you lay like a king atop your mound of coats. As you say goodbye later at the front door, kiss her cheek with just a little less indifference than you used to. You'll be seeing her at the next family function, and you'll want to do this again