Where's the pun here?

[Vibovit]

I was reading an article and I came across such a sentence -

We all sin, but is any sin separable from the sinner, or vice-versa (no pun intended!)?

This bit caught me out. What pun does the author mean?

[mykwyner]

The word "vice" is sometimes used to describe sinful behavior such as gambling, fornication, excessive alcohol use, drug use, etc.