"What's the big idea?" is a phrase commonly used to express surprise or irritation in response to someone's behavior. However, there are many other synonyms that can be used to convey similar sentiments. Some alternatives include "what's the meaning of this?", "what's the matter with you?", "what's your game?", "what's your deal?", and "what's your problem?". These phrases can be useful in a variety of situations, from addressing unruly behavior to expressing frustration with someone's attitude or actions. Whether used in a casual or formal context, these synonyms for "what's the big idea?" can help convey strong emotions and assertiveness to get the point across.
