Error reporting. Yeah it is a pain to come up with something that users will understand. As devs we need meaningful stacktraces so we can diagnose the problem but the normal person doesn't care. Also not having consistent messages looks terrible for the user's experience.

I hate it when there is no standardized error messages and/or json structure between teams or individual members of said teams. Why should we have 10+ different structures to code for in our apps? There is RFC 7807 for a reason. It has a defined structure plus accounts for custom properties. If you are a c# developer, check out the ProblemDetails class. It has made my life easier and I can guarantee everyone that all of my team's projects return this structure.