I had a less experienced person with me looking at some code.

I pointed out that a particular section of code is shit; just bad form, hard to debug and generally unpleasant to work with. I noted that the person that wrote this didn't really know what they were doing, sure the code works and has been working for a long time, but this is not how we would do things.

They asked "wow, who wrote this?" I replied "it was me 13 years ago"; it is a great ice breaker, in a non-critical part of the system, new people realize we all have to start somewhere.

It also allows me to go over the standards we use, why we use them and how to simplify debugging.