Meaning:

“岁月,” which literally means “months and years,” refers to “time,” “是” means “is,” “把” is a unit of quantity, and “杀猪刀” means “pig knife.” This saying, often used by Chinese netizens, is a humorous way of saying “how time flies” and “how a person’s good looks can fade with time.”

Example:

A: 这照片上的帅哥是谁？

Zhè zhàopiān shàng de shuàigē shì shuí？

Who is the cutie in this photo?

B: 是我念大学的时候。

Shì wǒ niàn dàxué de shíhòu。

This is me back in university.

A: 不是吧？你那时候真那么瘦？

Búshì ba？Nǐ nàshíhòu zhēn nàme shòu？

No kidding! Were you so slim at that time?

B: 岁月是把杀猪刀啊。

Suìyuè shì bǎ shāzhūdāo a。

Now you see how a person’s good looks can fade with time.