Really interesting overview of Iron, Jane Street's code review tool: https://youtu.be/MUqvXHEjmus
It makes a compelling argument for tracking diffs over time, nested feature branches, and encouraging reviewers to add their own patches.
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I've started keeping a list of particularly interesting bugs and patches that I've worked on: https://github.com/Wilfred/interesting-code
The time that I once removed *a single closing paren* in Emacs is still my favourite.
Over a sufficiently long time horizon, all code you write is legacy code.
It's really satisfying to use a profiler for the first time on a project. I always find a big performance win with only a small code change.
It's never the code that I expected to be slow, however!