For a week+ I've been listening to a senior dev ("Bob") continually make fun of another not-quite-a-senior dev ("Tom") over a performance bug in his code. "If he did it right the first time...", "Tom refuses to write tests...that's his problem", "I would have wrote the code correctly ..." all kinds of passive-aggressive put downs. Bob then brags how without him helping Tom, the application would have been a failure (really building himself up).
Bob is out of town and Tom asked me a question about logging performance data in his code. I look and see Bob has done nothing..nothing at all to help Tom. Tom wrote his own JSON and XML parser (data is coming from two different sources) and all kinds of IO stream plumbing code.
I use Visual Studio's feature create classes from JSON/XML, used the XML Serialzier and Newtonsoft.Json to handling the conversion plumbing.
With several hundred of lines gone (down to one line each for the XML/JSON-> object), I wrote unit tests around the business transaction, integration test for the service and database access. Maybe couple of hours worth of work.
I'm 100% sure Bob knew Tom was going in a bad direction (maybe even pushing him that direction), just to swoop in and "save the day" in front of Tom's manager at some future point in time.

This morning's standup ..
Boss: "You're helping Tom since Bob is on vacation? What are you helping with?"
Me: "I refactored the JSON and XML data access, wrote initial unit and integration tests. Tom will have to verify, but I believe any performance problem will now be isolated to the database integration. The problem Bob was talking about on Monday is gone. I thought spending time helping Tom was better than making fun of him."
<couple seconds of silence>
Boss:"Yea...want to let you know, I really, really appreciate that."

Bob, put people first, everyone wins.

Gave boss inside into JSON output for a system he never even sees or uses. Now he suggests changes to that JSON that aren't relevant nor possible...