Spoiler (i.e. the answer to what to do w/ those Golden Pantaloons in BG1)
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If you talk to the Nobleman, then he assumes that you are the cleaning service and he gives you his Golden Pantaloons to clean. You have a choice of replies--choose the one that says something along the lines of "Yessir! Pantaloons pressed and ready by tomorrow morning or breakfast is free sir!" and he hands you his pants.
Talk to him again (at any time, even immediately after he gives you the pants) and you'll get an amusing reply from him and a small (very small) amount of XP. If you have a high enough Charisma and/or Rep, you may even get a tip.
Of course, if you stole the Pants from the nobleman instead of recieving them from him, I don't know if this would work. Try to talk to him anyways.
Another Spoiler!
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Question about the Golden Pantaloons & the Big Metal Unit: since you lose *all* your items at the beginning of Baldur's Gate II anyways when you're in prison, would it not matter if you sold the Pants/ditched them/gave the Pantaloons back to the Nobleman/whatever? Where do you get the chance to pick up the Golden Pantaloons again in BGII?
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"He who controls the past, controls the present. He who controls the present, controls the future."
(G. Orwell, Nineteen Eighty-Four)