A gentleman is rare those days. A gentleman with some admirable bad boy tendencies is even rarer. It depends on the bad boy tendencies. Some I admit are shallow, like driving fast and skillfully a car or a motorbike, having tattoos, some muscle and long hair and an alternative sense of style. Some are fun, like liking to travel, or to try new things, to dare going out of your routine. And some are more meaningful, like having values and protesting about them, being your own person, not doing things because they are popular, being a volunteer, risking your life to save others.
Depending on what you mean by "bad boy" behavior. If he is an all around nice and good guy, I don't mind things like letting loose and having a few drinks with his friends or doing reckless "boy" things and stuff like that. I think a nice and very "goody-two shoes" is boring but I do look for really good, kind guys. So letting loose and having fun from time to time is okay but nothing too extreme.
to me, a "bad boy" is a teenage boy who's rebellious. I don't know what other people mean exactly when they say bad boy but I'd prefer to leave the juvenile behavior in the past and date a mature MAN at this point in my life.