What does this mean?

[Beeboy]

I was browsing through a gaming forum and there was a thread on how to boost Xbox achievements. One of the pointers it gives is this:

Quit Being An Asshole – no one likes being spoken to as if they're your pet monkey so stop yelling and talking down at them. The same goes for those who like to kick others out of games just for making the simplest of mistakes. The world if full enough of little Hitler’s as it is, no need to act like another one on Live is there?

What does the author of the guide mean when he says "no one likes being spoken to as if they're your pet monkey"? Or when he says "little Hitlers"?