Respect running code
One big red flag in a developer for me is when they complain about how much some old code sucks, when that code is still running and doing its job.
Shitting on running code tells me that a developer has little respect for the work that came before them, and little empathy for the developers who wrote that code, under different constraints, with different tools, in a different time. It’s good to want to improve things! But it should be done with a healthy appreciation of what already works.
Can old code become obsolete? Sure, but that happens after they are replaced by something better, not while they’re still operating (and we all know not every replacement is actually better).
Technology marches on. People learn new ways of solving problems. Tools improve. Organizations and resources change. To judge something written many years ago against the circumstances of today is misguided and—dare I say—disrespectful of those who came before.
PS: And don’t shit on old code even after they’re obsolete. Treat them with respect. Thank them for a job well done, and let them take their place in the history books.