I don't do this. It can come back to bite you in too many ways, such as

• clients reviewing code and thinking you're unprofessional
• clients thinking you're being rude about them (even if you're not)
• bugs being harder to track down because your replacement is left searching a mountain of code for things like "whoops!"

I'm not saying I haven't done that sort of thing before; I just try not to do it now.