My personal favorite (and most humiliating) is:
"I like you and all. I just don't like you enough." Ouch. Same to you, buddy.
wow. i like this one.
"Insisting on monogamy just shows you are needy and insecure."
that sounds like something copied from a sitcom.
Those are great! I think I've heard some version of all of them. How about these?
"I just broke up with my girlfriend because I don't want a commitment."
"My girlfriend of 5 years and I broke up last month, but we are still best friends."
Dizzy wrote: "I never call you because I really only want to hook up."