The expression dog eat dog does not refer to canine cannibalism but to an intensely competitive situation: one in which people are willing to hurt each other in order to gain an advantage or win.

The pain inflicted in such a situation usually isn't physical, though; you&'ll often hear the expression dog eat dog used to describe a particularly cutthroat business like investment banking or entertainment.

Check out these examples to see how dog eat dog is used in cases where one must fight to survive or get ahead:

Especially somewhere like London, it's a dog eat dog world and you've really got to fight your corner. (BBC)

The competition to land Inc.'s HQ2 operations was dog eat dog in more ways than one (Wall Street Journal)

Doggy dog is a simple mishearing of dog eat dog. It may owe some of its popularity to the chorus of Snoop Dogg's 1993 debut single "What's My Name," which repeats the phrase a number of times. The cartoonish, singsong quality of doggy dog sounds silly and playful, though, conveying the opposite meaning of dog eat dog, which evokes a cruel and selfish struggle.

Doggy dog is not common in print, but does show up in speech and student writing fairly frequently. The examples below highlight some misuses of the phrase.

In his disciplinarian moods, Harry reminds them all that life is "doggy dog," his own squirrel-lipped version of dog-eat-dog. (Time Magazine Archive)

As Ben Zimmer points out, "doggy dog world" is more of an "eggcorn," defined as a word or phrase that is used by mistake, usually because it sounds similar to the original word or phrase. (Columbia Journalism Review)

If you're still barking up the wrong tree, try to visualize the image that dog eat dog evokes (yuck!) and you won't forget that it means "competitive and cutthroat." Who says you can't teach an old dog new tricks?