When someone "blew one cool", it means they lost their temper or composure. There are several synonyms for this phrase, including "flew off the handle", "lost it", "went ballistic", "had a meltdown", "blew a gasket", or "flipped out". Each of these phrases implies that someone has reacted in an extreme and uncontrolled way to a situation, often resulting in negative consequences. It is important to keep calm and composed in difficult situations, so it is helpful to have these synonyms on hand to describe when someone has failed to do so.