Linguistics Question

In other languages where most nouns have gender, what do people do if the nickname of a person has a gender different than the sex of the person. This wouldn't really be a problem for nicknames based on adjectives or animals whose genders can change. But what about nicknames based on inanimate objects. For example, Tom Delay is known as "the hammer." If hammer is feminine, wouldn't that cause problems? (I wish I knew of a good example, where the gender and sex do not match. The Hammer in Spanish is El Martillo.) Let me know if you have an answer or a good example.