A fun, friendly, relaxed, joking and laughing environment does not define or constitute harassment. However, if the jokes, comments or gestures are rude, disrespectful and offensive, then it constitutes harassment. That leads me to another common concern and question. Of course not. Of course you can.
Harassment requires that the conduct be unwelcome.
The concern arises and the conduct becomes harassment if others in the office overhear the jokes or comments. They may not share your sense of humour and will find your conduct offensive and unwelcome. Furthermore, be sure that all those whom you share your comments with do in fact welcome this conduct. Perhaps they laugh because they are uncomfortable. Yet another concern is whether criticizing an employee's work is now going to lead to allegations of personal harassment.