My gf was laughing everything the kickboxing instructor said! Do I have a right to get mad?

Today my gf laugh at everything the kickboxing instructor said today! Me and her take that cl twice a week.. Got pissed cause even I dont get that much laughter from her! Wouldn't that bother you? Don't wanna be over jealous but I even tried to find something in the guys jokes and I laugh at everything... And she was the only one laughing out of everybody! Wouldn't that bother you?