bootleg adj. inferior, unappealing, worthless. (source: Double-Tongued Dictionary)
Further reading
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What about bootleg recordings of concerts and jam sessions that are highly prized by fans? Those are considered priceless.
That’s a different, far more common meaning that’s well-covered in dozens of other dictionaries and so is not within the purview of this site.
When my daughter started saying it I thought it sounded stupid because I had never heard it used that way. But then again it’s like saying “bogus” in sort of the same way. Stupid, lame, etc. I’m sick of everything being “ghetto”, most of these kids have never seen a ghetto in their lives.