There is no one perfect line that will inform but not scare off every guy. Just like there is no perfect way for a guy to say "I dumped my ex-wife because she wouldn't have enough sex with me". Some people are going to be put off by the concept no matter how you say it. Some are going to challenge whether it is true.

If you scare a guy off, that just means you didn't waste any more time with the wrong guy. The right guy won't be scared off.

When you can see it coming, duck!