It depends.
Sometimes a person will say "just kidding" only to defuse the social blunder that would be perceived as being made if the statement involved were not considered a "joke." It may very well be serious, as everyone familiar with the parties involved probably already knows.
I know of a situation where someone was punched "in jest", but the punch caused serious hurt even so. Witnesses even remarked on the power in it.
If it is very personal, chances are it is not really a joke--unless all parties involved are in agreement as to the nature of the joking. (Yo' mama is so ... jokes, for example, are usually not meant to be taken personally, but are meant to show off the teller's ability at a kind of word play.)
Sometimes a person will say "just kidding" only to defuse the social blunder that would be perceived as being made if the statement involved were not considered a "joke." It may very well be serious, as everyone familiar with the parties involved probably already knows.
I know of a situation where someone was punched "in jest", but the punch caused serious hurt even so. Witnesses even remarked on the power in it.
If it is very personal, chances are it is not really a joke--unless all parties involved are in agreement as to the nature of the joking. (Yo' mama is so ... jokes, for example, are usually not meant to be taken personally, but are meant to show off the teller's ability at a kind of word play.)