Why Do The Worst Guys Give Us The Best Sex?

There are about a million different ways to define a relationship without actually dating someone. You can be friends with benefits, hookups, booty-calls... need we go on? There is definitely a time and place for each kind of 'situation-ship,' but why does it seem like the people who give the most consistent good d*ck are never the good guys? Is it because we all mysteriously love bad boys? Is this an 'us' problem or 'them' problem? Perhaps some mysteries are better unsolved.