The Bronze Pantalettes are one of three sets of metallic pantaloons scattered throughout the Baldur's Gate trilogy. They serve as easter eggs, but if all three are gathered across the three games, they can be turned into the Big Metal Unit near the end of Baldur's Gate II: Throne of Bhaal.
The Bronze Pantalettes may be found in Abazigal's Lair in Baldur's Gate II: Throne of Bhaal. When discussing the Scroll of Reversal with Iycanth the Mad, he will point out a set of petrified adventurers - Bondari, Nanoc the Barbarian, and Tim Goldenhand - and suggest the player send them instead if they think that retrieving his Beholder Eyestalk is beneath them. If the party of amateurs is restored with a Stone to Flesh spell or scroll, they will retrieve the eyestalk, and also the pantalettes. Sending Bondari's party to fetch the eyestalk is the only way to obtain the pantalettes.
If a player collects the Golden Pantaloons in Baldur's Gate (game), followed by the Silver Pantaloons in Baldur's Gate II: Shadows of Amn and the Bronze Pantalettes from Baldur's Gate II: Throne of Bhaal, then the three may be taken to Kerrick the Smith in Amkethran, where he will turn them into the Big Metal Unit.