10. She's Not Wearing Underwear

How will you know this? Well, if you have to ask, stop reading the list now, because you have no chance. But if you do know how to ascertain this, and you're able to confirm that your date is sans unmentionables, then you're likely in good shape. If it's really f*cking hot, it could be that she's going commando for comfort alone, but if that's the case you'll be treated to such a show that you'll have no trouble laying yourself later should the need arise (puns always intended).

Of course there's also the occasion when she shows you—literally shows you—that she’s not wearing underwear. This is called the Basic Instinct, and it is fail-proof.