There's a group of chests/bones that NEVER drop rare item. It would be neat even if like once in a million they could.
*First Chests Tulors
*Daemon Home Chests on path to Ezelberoth
*Dart and his chest in UG
*USH Chest at Lich fight (OG drop location on MW)
And was thinking more along lines of % like trash mobs, not bosses. shrug