There's a level of Hell reserved for

• people who don't write tests
• people who remove a failing test, rather than fix their code so the test passes - because the test "must be wrong"
• people who don't reduce failing code to a minimal test case
• bug reports that just say "it does not work"
• people who roll their own version of X because it will be more efficient
  1. before finding out whether more efficiency is needed
  2. and write something less efficient than X anyway
• people who don't use CPAN