How do you sneak out of class early? With an AR-15
I don't think it's okay to joke about that. Do you really want to mock people who have lost loved ones?
People with sense of humor are laughing at you not with you
It sounds like you're making a joke about school shootings. While it may be funny to you, it can be harmful to other people. It might be helpful to listen to victims who have been harmed by guns in school so that you can tell jokes that are less harmful.