Bandicoot means: Any of various small marsupials of Australia and New Guinea, some with distinctive long snouts, of the family .. It is mainly Australian English and may not be understood outside that context. 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.