You can do better. It started one night when we realized that we were both pining over the respective guys that we were seeing (or maybe more accurately, trying to see) and evaluating our own behavior towards them, asking what we could have, should have, would have done differently.
Then we realized that we could have, should have, would have done nothing. If the way these men were treating us was making us unhappy, then why should we be questioning ourselves? And "You can do better" was born.
We realized that if someone's behavior is a source of unhappiness or discontent, then not only would we be unable to change the person to make us happier, but it wouldn't even be worth the effort! So we made a list of everything that made us unhappy, everything that we should not allow ourselves to settle for, and said that if someone we were seeing belonged on the list, then we could do better. Sometimes it's funny, sometimes it's heartbreaking, but it's always true. And once it was written down, it was like a big dose of reality and empowerment rolled into one.
The purpose of "You can do better" is not to set impossible standards or refuse to compromise. "You can do better" is about not compromising respect and fulfillment. It doesn't matter if he's into you or not, but if he can't pull it together for you, then you can do better!
If he has followed through on exactly zero of his promises, no matter how small, then you can do better!
If, in the same sentence, he says he loves you and wants to marry you, but wants to date other people for a few months in order to be sure--and he says all this while you are in bed together, then you can do better!
If, after many dates, she refuses to commit to you and keeps saying "let's just see what happens," then you can do better!
If he moves to another city for business school, breaks up with you despite your offer to find a job and move with him, then offers as condolence that he is still willing to look over your resume for you, then you can do better!
If he tries to use moves on you inspired by Mystery the pick up artist, then you can do better!
If he normally does not have facial hair but shows up to break up with you sporting a mustache (something that looks like this: http://www.virginmedia.com/sport/galleries/famous-moustaches.php?ssid=3), then you can do better!
If he spends his month-long Panama vacation insinuating that he misses you and asking you to make fun plans when he returns, but then on the day he returns he texts you that "all he needs is to see you tonight" only to break up with you, then you can do better!
If your friends genuinely wonder if he is a sociopath, then you can do better!

If, immediately after you break up, he says that this experience will help you both to 'learn from this so we don't get hurt in the future,' then you can do better!
If he stops by to break up with you while his sister is getting her hair cut and says that he needs to go when she is done, then you can do better!
If he brags that he is almost 30 and hasn't matured past his teen years, then you can do better!
If he brags about stealing someone's tab at a bar, then you can do better!
If he starts freak dancing with another woman at the surprise party he threw for you, then you can do better!
If you can tell that he's thinking about another girl while you're in an "intimate moment," then you can do better!
If he's married, and tries to convince you that it "isn't a big deal," then you can do better!
If he pulls out his special massage oil for when girls come over on the first date, then you can do better!
If he asks for your number while you're giving a presentation to the substance abuse program he is in, then you can do better!
If he has a Georgia O'Keefe painting on the wall because "he wants to show you how much he loves vaginas," then you can do better!
If he wants to tie you up on the bed he bought specifically for this purpose--and it's your first date, then you can do better!
If he think it's sexy for you to wear his ex-girlfriend's prom dress, then you can do better!