Seriously, do they teach guys this phrase at the same class where they learn to put their hands behind their heads and smirk when getting a blow job? Well, there are a few things you all need to know that they didn't teach you in class.
One of them is that we women know that "I can't give you what you deserve" is a cop-out of astronomical proportions. Even if the woman you tell it to is too distraught to understand its underpinnings, her best friend knows and she is going to rat you out. This line is designed so that the guy feels like a hero of sorts - sacrificing being with the girl so that she can find someone better, someone who will fulfill her every dream of happiness. Fact is, guy is selfish and self-serving and doesn't care to sacrifice anything of himself to make the relationship work.
Has a girl used the line on a guy? I'm sure, and in that case, the girl is selfish and self-serving too. Right now though, I've got a friend who is hurting more than I can even imagine and that line started it, just like it did for me over three months ago. So forgive me if I'm feeling a little anger pointed in the direction of the general male population this evening.