The phrase "go wacky" can be replaced with a variety of synonyms and related terms to express a similar concept. Some possibilities include "go crazy," "go nuts," "lose it," "freak out," "act bizarrely," "go off the deep end," "fly off the handle," "go wild," "become unhinged," "lose your marbles," "flip out," and "go bonkers." These phrases all convey a sense of someone's behavior becoming erratic, unpredictable, and potentially dangerous or alarming. Whether used in a serious or humorous context, they can help to convey a sense of heightened emotion and unusual behavior.