Antonyms for the phrase "did to a t" could include "missed the mark", "did haphazardly", or "did carelessly". When someone says they did something to a T, they mean they did it perfectly or exactly as it should have been done. Using antonyms can imply that the task was not completed to the best of someone's ability, or was done with less precision or attention to detail. It's important to consider the context in which these phrases are used, as different synonyms or antonyms might be more appropriate depending on the situation. In short, "did to a T" means perfect execution, while antonyms imply an imperfect or careless execution.