When a man is able to hook up with an entire group of girlfriends. The last girl is usually the hardest because by now she has heard rumors of the manwhore characteristics of the guy and the bonds she has with her friends might overcome any smooth attempts of said manwhore.
Alcohol is almost always required.
After hitting it with Hilary, Heather, and Jenna, I attempted to complete the set with Ashley. Then Hilary talked to Heather and told Ashley how much of a manwhore I am, and now she won't talk to me.