"Genericide" Losing your trademark because it becomes a generic term. For example Thermos which was a brand name, then in 1963 the courts declared it a generic term for a vacuum flask. Escalator, previously a trademark of the Otis Elevator company.
Xerox has spent a lot of money trying to stop it becoming a generic term.
PS. Heroin used to be a trademark of Fredrick Bayer & Co