You have committed a crime--at a minimum, it will be some type of vandalism or damage of (expensive) personal property. Depending on the circumstances, such as if your girlfriend or sister were intimidated or threatened by your action, you may also have committed a crime by threatening them as a well.You therefore *could* be arrested. Whether you will be depends on many factors: how it was reported to the police, whether you have a prior record causing them to take your actions more seriously, the guidelines of the local police department, even the personality of the officer(s) who took the call. Also, how you act if the police speak to you will affect what they do from there. The police might arrest you, might give a summons to appear, might simply talk to you. You should be prepared for the possibility of arrest.