6. DON’T Have Sex with Her Sister

Yes, there a couple of ways this would come about, all of them difficult to avoid, meaning take care.  Don't check out baby sis in any enticing positions, at all. If she's showering, sunbathing in the backyard, or having a slumber party pillow fight with friends, steer clear. Of course, this becomes an even larger problem if your girlfriend is an identical twin, because you have to contend with mistaken identity, as well as your own horndoggery.

Pro Tip: Tie a colored bracelet of twine around the twin’s left hand as she sleeps to tell them apart. Don’t have sex with her while doing this.

Photo: Identical Twins, Roselle, New Jersey, 1967, Diane Arbus