Not specifially one but a couple of minor mentoring moments.

I started out at a rather small company (<10 people) with a completely new language to me (Perl).
I had some trouble following along some tasks since I wasn't familiar with Perl or generally backend stuffs at all.
So the person that was supposed to "mentor" me was just giving me tasks without any hints of how to do things, this is where my "true" mentor came in to play.
I asked him a couple of things after a few unsuccesful searches on the internet and he always seemed to have the answer to it right away! It seemed like he knew everything and I really appreciated his patience and help. He did point me in the right directions when I needed it.

He left the company about 3 months ago and I still somewhat miss his mentoring existance, as he wasn't only a code but also a life mentor.

I really hope that one day I can be just like that guy, helpful, patient and be a mentor for someone else. :)