"haddest crack" is an informal term used to describe someone who is skilled or proficient in a particular area. Some synonyms for "haddest crack" include "expert," "master," "pro," "ace," "whiz," and "genius." These terms all convey a high level of proficiency and knowledge in a certain field. Additionally, words such as "accomplished," "proficient," and "skilled" also indicate a level of expertise. Overall, there are various words that can be used to express the concept of "haddest crack," depending on the context and the level of proficiency one is trying to convey.