Speed demon:
Chiefly US, informal: someone or something that moves or works very fast.
“Speed demon（速度魔鬼）” 实际用来比喻 “工作、办事速度很快，行事敏捷的人或物”，有 “雷厉风行，风驰电挚” 的意思，也可以指 “高速驾车的人”。
例句
The barista is such a speed demon that he can make a perfect cappuccino in half the time of other people.
这位咖啡师干活特别麻利，能用别人一半的时间做出一杯很棒的卡布奇诺。
My new laptop is a speed demon and can run some programmes really quickly!
我新买的笔记本电脑速度快如闪电，运行一些程序的时候真的很快！
Sandra is such a speed demon behind the wheel. To be honest, she scares me when she drives.
桑德拉开起车来真是风驰电掣。说实话，她开车时令我害怕。
