"lagerphone" means: A generally homemade percussion instrument consisting of crown cap beer bottle tops loosely nailed to a pole (often a broom handle) and a bo.... This is a fairly neutral word with no inherent risk attached. There is no real cause for parental concern; it is descriptive vocabulary rather than something dangerous. If your child uses it, context will usually make the meaning clear. A brief, curious question about where they heard it is generally enough to know whether to follow up.