"Flew the handle" is a colloquial expression often used to describe someone who has lost their temper or become incredibly angry. There are many synonyms that can be used in place of this phrase, including words like "lost it," "went ballistic," "blew a fuse," "flipped out," and "had a meltdown." Other similar expressions include "popped a vein," "hit the roof," "went off the deep end," and "lost their cool." Regardless of which word or phrase is used, the meaning remains the same - someone has become incredibly upset and has likely acted out in some way.