Of course, this is a very subjective subject. My findings are mainly based on the dogs i have come in contact with; many of whom are problem dogs at home who are brought to daycare because it is cheaper than hiring a trainer. Also, many breeds are owned by people who should NOT own a certain breed either because they are too busy/lazy to give the dog what it needs or by just being totally oblivious (see note above about witnessing the depth of human stupidity).
If your breed of choice is on this list and is perfectly well behaved and amazing, that's awesome. I would love to meet him/her. Truly I know that some of my issues with the dogs below come from ownership issues and not from the breed itself (and in that case i applaud you for being an above average owner).
...but you still couldn't pay me to own one.
So please, do not take the following as a stab in the heart if your breed is listed, ok? :)
Number 1: American Bull Dogs
These dogs are my number 1 pet peeves at work. 99% of them we have severe problems with, mostly because their owners are oblivious to their dog's social problems.
Number 2: Mastiffs (any variety)
Number 3: Old English Bulldogs
Number 4: Boxers
Number 5: St. Bernards
Number 6: Rottweilers
Number 7: Beagles
Number 8: Huskies
Number 9: German Shepherd Dogs
Number 10: Doodles (any poodle mix "designer breed")
Number 11: Golden Retrievers
Another breed that is supposed to be intelligent I strongly believe that the brains have been completely bred out of this dog. I need a dog with a brain.
Runner up: Labrador Retrievers.
Another dog that has suffered from having the brains bred out. I think I could own a lab, because I know that I would be able to turn his/her mushy brain into something worthwhile and Trophy is half lab... but they are LOW LOW LOW LOW on my list.
Ok... so what dog could you never own?
(Follow up, dogs I must own before I die coming soon!)