It would be personal if I was trying to change them as a person, if that makes sense. Offering constructive criticism should not give someone cause to decide I don't like them as a person, which is what a lot of people do.

Case in point: our fencing club recently had to ask their treasurer to step down. He's decided it's because the VPs don't like him, which is precisely the opposite of the case. They don't like how he was failing in his duties, but as a person they really do enjoy his conversation and company. The decision to ask him to step down was not a personal one, but a professional decision necessary for the good of the club.

Does that help clarify my point? Some people take professional criticism personally, and personal criticism not at all.