Dogs are often considered as man's best friend. However, the aforementioned phrase has a certainly negative meaning. The same phrase exists in French as well.
Other negative phrases with dogs include work like a dog, die like a dog, a dog's life, etc. How long ago in the English language does this negative connotation date?
Best Answer
Yours is an interesting question but, as explained in the previous answers and comments, since dogs were considered wild and possibly dangerous animals till a few centuries ago, I think that probably the issue is: when did expressions about dogs change from negative to neutral or positive?
Also, phrases that indicate the treatment of dogs show that they were considered to be of little worth:
The language relating to canines took a turn for the better later in the 18th century.
Source: The Phrase Finder