Resist the temptation to hit him with your lecture the minute he walks in the front door. Instead, welcome him home, give him a snack, and hear about his day. Later, after he's had some down time, tell him you need to discuss a problem with him. Instead, discuss issues privately with your child. Watch how you say things.
Parents often have the tendency to either clam up or blow up.
Neither is wise. A mom who simply keeps her mouth shut all the time can breed insecurity in her child because the child won't know where she stands or what her parent really believes. On the other hand, it's far better to wait and think through how to say something than it is to blow up and later regret how you handled the situation. Notes can be saved and notes don't demand a response. Then stand firm.