I see a naked man I don't know standing over my daughter, I assume he is attempting to rape her. Period. Bang.
If it's a boyfriend I have never met, well, that sucks. But again, the "reasonable person" is going to be drawn from my area, and I know what the majority of people here would say.
No, it won't be drawn from your area--it will be whatever the law defines it to be in the jurisdiction in which you are tried. You will likely be forced to argue that you reasonably believed the man was committing a felony, not that a naked man with your daughter is presumptively committing a felony.
If this may actually be an issue for you (daughters at home, for example, and a fear that a boyfriend might show up), it might be wise to consult an attorney to have this verified to your satisfaction. You won't like what you hear, but at least you won't be under the illusion that your presumption of danger in these sorts of situations will protect you from very serious legal consequences.
The story you posted, btw, is a completely different situation. I will highlight the key facts:
Michelle Carroll was upstairs in her Lauderhill town house when she heard her 7-year-old son yell that there was a man in the house.
''She asked him to leave several times and then he wouldn't leave,'' said her cousin Lindey Carroll. ``He walked toward her, and she shot him.''
Notice that she has an alert from her child, tries to get him to leave, and he's uncooperative, and naked on top of it.