Early versions of SAP R/3, using the thick desktop client. Took one day to register one month of work, when work was 20 8-hour days of exactly the same billing code.
Any network code written or endorsed by The Lennart, especially DNS or DHCP related. (the idea of a init replacement that can restart processes cleverly is not a bad one, only implemented better by others, like on AIX, since 1994 or so)
Any license management software, case in point flexlm. (one can argue that it is successful, because its job is to prevent people from running software, and there it certainly is an overachiever.)
H-PUKES (AIX wannabe, with one of the worst compilers ever almost-bundled. Would have been OK if free. Was not. )
Solaris manpages written by people who would rather write a dissertation using Complicated Words than tell people how to run the fucking program.
Software without sensible defaults.
I've been using OS X since about 2003, and am still with it. I mostly like it, but: Every release they make it less Unix and more iOS, and we complain, and continue using it. As if we're slow-boiled toads. I need to stick kexts (kernel modules / drivers) into mine, and that is more and more painful, and often accompanied by "you should really reconsider that" warnings.
I have very few complaints with OpenBSD and FreeBSD. If I can, that's what I run.