hatter 意为“制帽者”，as mad as a hatter 这个习语用来形容人发疯了，可以意为“发疯，气疯”。

【例句】
The way he dressed for the event, he must be as mad as a hatter.
他参加活动的打扮，一定是疯了。

He wants to build a plastic car and drive around the world! Talk about being2 as mad as a hatter!
他想建造一辆塑料车，开着它环游世界！他真够疯狂的。