When is a joke not a joke?

Hey, some of you guys might think this is stupid but people have there own opinions and this is mine. 

 So I can take a joke but when is it not a joke anymore where is the line and how do you know you have crossed it. 

I know I'm guilty of saying things in a joke and then crossing the line and having to deal with the consequences. But everyone will cross the line at least once in there life some more than other. Is it appropriate to call some one a slag or a slut for a joke? I don't think it is some people can shrug it off and forget. I can do the first part but the second part te forgetting is hard. For me all I think about after that is did they mean it, was it a joke   

Personally I'm gonna try and stop saying thing that I don't mean and not let things slip out as a joke. 

Thanks for reading love you. 

             XX Freya Owen XX

                   Élan Beauty 

                        OXO