Yep, quite true. We Epirotes and them Makedonians bore the burden of defending the borders from Illyrians/Paeonians/Thracians, paying a very heavy price for it, and the southrons didn't even believe we were Greek. (Who do you think stood watch while the southrons had their golden age and then fought each other-There is a reason why only Persians and Gauls broke through and reached down south)

(To the delight of our neighbours throughout the millenia who have gone on to claim our name and identity for themselves)

I guess such a trait could very well exist in the sense " You arrogant... (insert favorite swearword, probably one to do with female genitalia). Here we are defending you from outside enemies, we fought our common foe to Indus and back, and you deny us our very own ethnicity? Well (insert ugliest form of "copulate") you right back. From now on, we hate your (another favorite swearword, this one with unspeakable implications on one's mother) guts!"

Still happens you know, but in footy terms. Athenians get some ugly treatment in Thessalonike, like their car's license plates spray painted red or black, or even pink, having a pitta with just tomatoes and a straw in them, rather than meat, (a "south" greek idiom that), etc.