One antonym for the term "most nasty-tempered" is "gentle." A gentle person is known for being kind, patient, and peaceful, making them the opposite of someone who is most nasty-tempered. Another antonym is "calm," as someone who is calm is composed, collected, and level-headed, in contrast to someone who has a bad temper. The word "sweet" can also be considered an antonym of "most nasty-tempered," as it implies a person who is pleasant, amiable, and easy to get along with. Overall, there are many antonyms that can describe someone who is not most nasty-tempered, including gentle, calm, and sweet.