One that comes to mind for me: "Whatever doesn't kill you makes you stronger" is not always true. Maybe even only half the time! Are there any phrases you tend to hear and shake your head at?
I'm so sorry! He/She's (never done that before)/(usually so much better behaved)!
Said by idiot dog owners who either let their dogs run off leash, or don't pay enough attention when they are leashed, which then attack people or other dogs.
If you don't have enough time or care to raise your dog properly such that it obeys basic commands and is familiarized with the world beyond your apartment/yard, you should be exercising far, faaar more caution and restraint.
Personally I don't think such people should even be allowed to own dogs if they can't train them properly.
So many people just take their dogs to a dog park and let em loose!