What is the ruling on dealing with something cursed by a person, such as a car, a pen, or an item of clothing, and is it permissible to use it or must it be disposed of?

There is no prohibition against benefiting from a cursed object. The intent of the prohibition against associating with the cursed she-camel in the noble Hadith (definition) is specifically against its association with the Prophet, peace and blessings be upon him, and not a general prohibition preventing other actions such as selling it, slaughtering it, or riding it. Furthermore, scholars have warned against cursing animals and inanimate objects, and that if a curse ascends to the sky and its gates are closed, then returns to the earth and its gates are closed, it reverts to its utterer if it finds no one deserving of it.