I like dogs, a lot. But seeing what friends go through, here are the worst:
1. Dog vomit on the carpet. Again.
2. Dog hair everywhere, dog nose prints on every glass surface, all the time. (This one is not so bad, you know what to expect, at least)
3. Insisting that your dog is at least 2 years before being neutered, to have a "natural" hormone system, then having to put up with dogs in heat, teenage dog attitude issues, etc.
4. Dog that turns out to be half blind and wildly barks at everything, because it doesn't remember the postman (who now has put a dangerous dog note on your address file, just from hearing your dog through the door)
5. Finding out you are highly allergic about 18 months in to a dog that you wildly love.
6. Finding out your dog has not only dominance behaviours that make the dog park difficult, but possible, but now growls and acts aggressively to the new baby, so you need to rehome her after spending $6000 and 8 months on dog / owner training.
7. Dogs chew up your walls. I met a dog that would chew drywall and wood trim while owner were away from home. big holes in the laundry room and the stairwell where the dog would be kenneled.
8. Dog sitters needed for the weekends away, or long day trips.
9. One friend ends up kenneling her dog for a week at a time, just to get things done, like painting the house. Fees are enormous, several weeks out of each year.
10. Some dogs need extra grooming to keep healthy -- something about glands and all that..
My biggest reason not to have a dog -- I work out of the home for 10 hours per day. Some dogs are fine, but some dogs are such people pleasers that this is utter hell for them.. I can't stand the thought of leaving a dog with that nature alone for so long. It breaks my heart when I see neighbors doing this.