The phrase "all wet" is an idiom that means completely wrong or mistaken. There are several synonyms for this phrase, including "off-base," "misinformed," "incorrect," "clueless," and "mistaken." Other possible alternatives include "untrue," "inaccurate," "fallacious," "fictitious," and "bogus." Depending on the context in which the phrase is used, other possible synonyms might include "unfounded," "unsupported," "baseless," and "erroneous." Regardless of the specific synonym used, all of these terms convey the idea that something is completely and thoroughly wrong or mistaken.