Jitbag means: A British insult - crude, punchy, and mostly used when someone's being a complete idiot or acting contemptibly. It's the kind of word hurled in frustration rather than calculated malice, sitting in. There is no real cause for parental concern; it is descriptive vocabulary rather than risky behaviour. 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.