The phrase "wildly irrational" can be substituted with a variety of synonyms to convey the same meaning. Some possible options include "utterly illogical," "completely nonsensical," "totally irrational," "entirely unreasonable," "absolutely absurd," "unfathomably senseless," "wholly erratic," "deeply irrational," and "incredibly illogical." Each of these synonyms emphasizes the extreme nature of the behavior or belief being described, highlighting the fact that it is not just a little bit irrational, but completely and utterly so. This can be a useful way to convey a sense of shock or surprise at the irrationality being described, or to emphasize the magnitude of the irrationality in question. So, these synonyms can come in handy in various situations.