虎头蛇尾的英文：
[Literal Meaning]
tiger/head/snake/tail
The head is as big as the tiger's and the tail is as thin as the snake's.

[解释]
开始时声势很大，到后来却变得很小。

[Explanation]
a fine start but a poor finish

[例子]
无论做什么事都不要虎头蛇尾，一定要有一个完美的结果。

[Example]
We should not make a fine start but a poor end no matter what we do. We must have a good end.

[英文等价词]
In like a lion, out like a lamb.

A flash in the pan
虎头蛇尾

Start off with a Bang and end with a whimper
虎头蛇尾

I've asked you to do this for me because I know you're not a quitter.
我要求你为我做这件事,因为我知道你做事不虎头蛇尾。

The mountain has Brought forth a mouse
虎头蛇尾

The story begins dramatically but the plot peters out before the end.
这故事有些虎头蛇尾.

Whatever we do, we must see things through from beginning to end, and must not do things by halves.
我们做任何事情都要善始善终，不要虎头蛇尾。

I must postpone the reply for one moment, or we shall have an anti-climax
我必须推迟片刻，暂不作答，否则我们将虎头蛇尾了。

He is of a variable mood; he never finishes what he starts.
他这个人朝三暮四，做起事来总是虎头蛇尾。