Anyone can call him/herself "Christian."
Originally, it was a word applied to a person as that of a tradesman, something of profit that one is performing and/or purveying; not just professing a state of mind.
"Regenerated" means a total renewal of one's being, to the People of The Way, spiritual rebirth that affects one's behavior toward sin.
Something then unregenerate simply cannot wrap their minds around, hence the constant accusation that if one is secure in their salvation, they look at it as a license to sin.