There are several synonyms for the phrase "nothing to do with the case" that can be used to convey the same meaning. One such synonym is "irrelevant," which indicates that something is not relevant or applicable to the matter at hand. Another synonym is "unrelated," which suggests that there is no connection or correlation between the issue and the topic under consideration. Similarly, "extraneous" can be used to indicate that something is outside the scope of the case or situation being discussed. Ultimately, all of these synonyms serve to convey the idea that something is not pertinent or germane to the issue being addressed.