Gertcha means: A classic Cockney exclamation meaning 'get out of here!' or 'go away!' - used to express disbelief, mock dismissal, or genuine annoyance. 'Gertcha' is pure working-class London dialect, the kind of. 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.