When your teenager says 'bruh', they mean it the way an older generation said 'dude' or 'man'. It's a filler word, an exclamation, a reaction. 'Bruh, no way' is shock; a slow 'bruuuh' is disappointment; just 'bruh' on its own is often exasperation. It does not necessarily mean they think you are male, or even that they are addressing anyone in particular — many teens say it to themselves. It is informal but rarely rude, and usually a sign your kid is relaxed and being themselves. Treat it as a verbal shrug, not as cheek.