Forbidden Taboo

''What did I tell you about reading from that forbidden book? Now you'll be cursed for life!''

The weapon, tool, gear, or other item someone (likely a member of the Main Cast) was warned against but still associates with, resulting in inevitable badness. Whatever the Forbidden Taboo may be, it shouldn't be messed around with or else consequences will be suffered. But since Plot Forced UnTrash, the Main Cast must go against their warning and mess around with it. The Forbidden Taboo might summon a baddie, rip a portal through spacetime and whisk everyone away to some pocket dimension of evil, curse someone, or cause a Nuclear Explosion.