You may well be an expert now working with "Application X"...
However the hair pulling was so much that you'd never add it to your resume (even though it might sound impressive) for fear that a future employer might think your the ideal candidate to "migrate", "integrate" or otherwise work with "Application X".
Feel free to elaborate on why... (e.g. their APIs change monthly, there is/was no API, etc.)
(made into a community wiki)
C++
Worked with it from 1990 (using cFront!) to 2000. Have no desire to repeat.
Plus, I suspect that I couldn't get through the level of interview that I would expect from a company where I'd want to work.
Visual Basic and basically anything to do with windows programming.
I suspect it WOULD in the end help me get a possibly better job, but I'm positive it won't be the job I want.
Created a device driver and a disk scheduler for linux.
Disk scheduler i could repeat. It really was fun. A device driver on the other hand... NO WAY.
That is not how i want to spend the rest of my life.
The issue isnt here with Linux per se. It just that i dont like the idea of dealing with user space and kernel space and all the registers and timings and buffers and DMA... it just keeps on coming and coming! The mail never stops!
I wasnt an expert on either of those by a long shot btw. Before any of you think im some sort of a linux guru.
Those for which I signed an NDA or required a security clearance for. The absence looks conspicuous, but usually interviewers understand why.
Even though I use VBA infrequently to automate tasks in excel, I don't list that on my resume because I don't want to be hired as a VBA developer. Replace VBA with any number of skills I have but don't wish to advertise as a "key" feature of me.
Further, I customize my resume based on the job listing so it's easier for the company to pick out the requirements and skills that match their position, so in general my resume contains very little relative to what my skills are. Those things can be discussed in the interview.
Do languages count? If so COBOL. It's insanely boring and (having it on your resume) makes people think you're old.
Meditech / anything having to do with the MUMPS programming language. Seriously, it's the single most mindblowingly awful thing I've ever attempted to be even marginally productive in. Check it out on the wikipedia: http://en.wikipedia.org/wiki/MUMPS
And how could I have forgotten the very first proprietary thing I learned to hate? The Progress 4GL/RDBMS. I was tasked with taking an MRO application written for a green screen using the Progress 4GL and helping to "web enable" it. Doing a simple export of a single table took hours upon hours for only a handful of megabytes of data. I honestly don't know which one I hated more. It seems that it's now been renamed the OpenEdge Advanced Business Language, which just makes me want to choke even more. Check it out on the wikipedia: http://en.wikipedia.org/wiki/OpenEdge_Advanced_Business_Language
Application - MS Commerce Server
Commerce server is a great idea gone horribly, horribly wrong. Pluggable, scalable, full featured shopping cart/inventory management system is a great idea. Pairing quirky, buggy, complex with being a complete black box (right down to the table structure, with 60+ columns per table named stuff like "cy_ois_omd") is where it goes wrong.
Language - PL/SQL
Oracles internal stored proc language. conventions like := for assignment drive me up the wall.
Like others who've posted answers here, I tend to leave out languages I have not worked with in a long time or have an extreme distaste for. Ironically, sometimes you end up having to work with them again (curse you, Java!), but I'd rather not be hired on the premise of developing in such environments exclusively. Obviously, I'd rather keep my CV short and sweet, and be hired for something that I'm already good at doing.
Also, I should note that I'm highly unlikely to submit my CV to a large company using automated document scanning to search for applicants by keywords. At this point in my career, I have settled into a fairly niche industry, and most of the companies in my field are smaller and will use a lot of human contact during the hiring process. As such, they're more interested in seeing "the meat" in a CV, not a huge list of buzzwords.
But as far as actual jobs or application development goes, you shouldn't omit anything. I'm not sure if this is the norm in all countries, but at least in some parts of Europe, it's considered highly suspicious to leave any time gaps in your CV/resumé. So even if you are unemployed during a period of time, you are expected to note as such. That said, the less-than-glorious jobs that I've worked over the years never get eliminated from my CV, but rather, every time I need to add something else, I edit down some of the older jobs or project descriptions on there.
Definitely Asterisk, the PBX from hell, coded by retarded monkeys on crack.
foxpro. I'm even reticent to put it here in case someone is trawling for coders... Besides, I really suck at it (because of utter lack of motivation to improve).
COBOL because I'm not interested in ever developing in it again.
InstallShield. Yeah, I created a few installation packages years ago. Wouldn't like to do it again.
HTML Help Workshop (or similar). Yeah, I created a few help manuals for the application I created installation packages for. Wouldn't like to do it again.
MS Paint Who cares?
Notepad They wouldn't understand the full potential of this tool anyway
Notepad++ Find me an employer who would understand the difference between Notepad and Notepad++
Paint.NET Well, you got the pattern ...
MS Access Where should I start?
Basic Good old Basic. My first programming language. I was at school and the computers were called Agat. It was like year 1989. If you were an Agat user too in the good old days, you get free daily upvotes from me. :-)
Fortran that was in the uni I believe
Turbo Pascal Can't believe I forgot about this one
Crystal Reports!
It is doesn't scale, leaks memory, doesn't play well with any technology but itself, and gives error messages that are far too generic to ever troubleshoot (leaving you to rely on brute force methods). Only a sadist would want to be the CR go-to guy/gal.
LaTeX, many people I know don't even know what it is, much less care if I can interface with it.
Java Swing (since I've seen Qt and Nokia promised they will release it under LGPL, I don't want to see Swing anymore!). There is also a nice project (an embedded computer for land-vehicle tracking) that was developed with an awful language (BASIC). I like to tell the first part and omit the second :)
Lotus Notes - in principle I like the idea. From a safe distance. Just not the execution.
ColdFusion - I'd rather work with a 'real' web development language.
Harvest source control and deployment system - "Software by Stephen King, User Interface by Salvador Dali". Can't recommend it.
CMD.exe scripting
I know way, way too much about CMD nuances, and hope to forget it all. I've written scripts that are:
PowerShell is the future!
I never put QBASIC on my CV when I left university, I was embarrased it wasn't a 'proper' language, despite learning it as part of my engineering degree course.
The second job I got (writing ASP) was for a company that had their flagship product written in QBASIC. My eyeballs popped out, and I just stammered, "no?!"
The truly vilest language I ever worked with was called A.M.
I hated it so much it was the main reason I left my job. That's not exaggeration, it really was torture to work with. Never mind understanding the language; how on earth can you survive day by day if you cant reliably use cut/copy/paste? The editor would interpret your paste operations as "do nothing to the subroutine currently being edited, but randomly remove some code from another routine where the programmer cannot see". I lived in fear of destroying the app I was supporting. It put you on edge all day.
Every spare moment was spent desperately trying to find a way to write another interface to the underlying database. I would have rewritten the app in my spare time at home if that had been possible!
Forté & UnifAce
(I haven't used UnifAce since 1999 but I still have random recruitment agencies offering me UnifAce jobs once or twice a year, it seems your card is marked for life at the merest mention of it)