As individuals? Nothing in particular.
One time though, a whole bunch of them came down, burned my city to the ground, salted my farm, and killed my friends....
...wait, no, that was Gone with the Wind.
On an Individual basis, I have found that Yankees are just as diverse as Southerners. Some Yankees are exceedingly polite, follow basic rules of curtesy, and practice the proper etiquette that should be displayed in mixed company.
Some Southerners are exceedingly rude, highly illcouth, illiterate, and generally ignorant.
In a general sense though, the majority of Southerners I've met are considerate, relatively well-mannered, honorable, and moral people.
And the majority of Yankees I've found to be slightly offensive, a little pushy, a little arrogant, and as a whole, the type of person I don't particurlalyl want to be around. (And that's saying something because I really love people)
All that being said, one of my best friends is from Pennsylvania. Granted, he's from a farm in Pennsylvania, but that's still pretty far north. My Aunt and Uncle live in New Jersey, and my cousins live in Chicago.
So yes, I have spent considerable time in both the North and the South. I'm not saying that I am uninfluenced by preconceived notions about Yankees, I am well aware of the stigmas my family holds against Yanks, but I feel that as a whole, a great many of them are proven true.