Jizzbag means: A coarse insult for someone considered stupid, contemptible, or worthless. The vulgarity is the point - it lands harder than more generic put-downs. Typically deployed in heated exchanges or used. It carries sexual or vulgar connotations; not alarming on its own but worth understanding the context your teen heard it in. If your teen uses it, context will usually make the intent clear. A short, curious question about where they heard it is usually all that is needed to know whether to follow up.