The phrase "went loco" describes someone who has become irrational, crazy, or out of control. There are several synonyms that can be used in place of this phrase, depending on the context. For example, someone could be described as going berserk, losing their mind, or freaking out. Other synonyms include going nuts, losing one's cool, or going off the deep end. In some cases, people might use more specific terms like having a meltdown or going ballistic. While the specific phrase "went loco" may not be appropriate for all situations, there are many other ways to describe someone who has become unhinged.