If you describe someone's behaviour as maniac, you are emphasizing that it is extremely foolish and uncontrolled.
lunatic
He could not maintain his maniac speed for much longer.
他不能太长时间地保持这种疯狂的速度。
maniacs
A maniac is a crazy person who is violent and dangerous.
The cabin looked as if a maniac had been let loose there.
小屋看上去像是被放任的疯子光顾过一样。
If you call someone, for example, a religious maniac or a sports maniac, you are critical of them because they have such a strong interest in religion or sports.
My mum is turning into a religious maniac.
我妈妈正在变成一个宗教狂热分子。