I found answers on many web sites and they differed too much so I decided to ask the community.
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I call him the devil because he makes me wanna sin… Urban Dictionary
A good-looking cheeky fellow.
Yahoo! answersSymptoms of being a handsome devil include
being good-looking, rich and a jerk. Often a playboy.
TV TropesThe very Devil, himself, is supposed to look amazingly-charming, and
can attract almost any woman. Therefore, a guy who's " devilishly
handsome / good-looking " is a man who looks so attractive, especially
to the opposite sex, that the women swoon over him, in huge numbers.
Yahoo! answersIt's a very common expression, used as a compliment of sorts. It is used to compliment someone, a man, but at the same time, usually to give a little jab, like saying "You're a handsome man, and you're very much aware of it. Word Reference
Best Answer
Urban Dictionary said
Yahoo Answers said
and
The Wordreference thread confuses the issue.
The first two say pretty much the same. The guy is handsome; so handsome that other men acknowledge it. The Devil part of the expression, when said by a man, can indicate some envy of this guy.
He is so handsome that women find him to be an instant temptation. If they are already involved in another relationship, then they may see him as an invitation to sin. Some can find him hard to resist.
But he also knows all that. So he flaunts it, and perhaps teases women with it, enjoying the effect on others. Some people might call that behavior cheeky.
Hope that helps.