- People getting angry at browser JS authors for coding in explicit support, or huge back-compat shims, for obsolete browsers and/or deprecated JS features.
- People getting angry at Perl authors for writing code that depends on a stable hash iteration order (changed in Perl 5.26 or something? I forget). There was an extremely vocal (tiny) minority of users raising a big stink about the change in that behavior and claiming that it would break the universe.
- C developers being criticized for coding to older (and often more verbose or tricky to use, but omnipresent) pure-POSIX macros and behavior rather than $latest_GNU_or_GCC_feature, which also had the pernicious effect of making things less portable, and damaging the culture of portability.
There are more examples, but you get the idea.