I used Perseus to select these texts, and the translations are from the Loeb collection.

 In Euripides Iphigeneia in Aulis 1400 , Iphigenia, the daughter of Agamemnon, says as she states her determination to die "heroically" so that the Greek fleet her father commands may sail off to Troy:

It is not right that this man should enter into battle with all Argos or be slain for a woman's sake. Better a single man should see the light than ten thousand women. [1395] If Artemis has decided to take my body, am I, a mortal, to thwart the goddess? no, that is impossible. I give my body to Hellas; sacrifice it and make an utter end of Troy. This is my enduring monument; marriage, motherhood, and fame -- all these is it to me. [1400] And it is right, mother, that Hellenes should rule barbarians, but not barbarians Hellenes, those being slaves, while these are free.

 Thucydides Histories 1.6 [Thuc. 1.6]. The fifth-century BCE historian Thucydides talks about uncivilized behavior of the Greeks and compares it to the mores of the Barbarians:

The whole of Hellas used once to carry arms, their habitations being unprotected, and their communication with each other unsafe; indeed, to wear arms was as much a part of everyday life with them as with the barbarians. [2] And the fact that the people in these parts of Hellas are still living in the old way points to a time when the same mode of life was once equally common to all.

 Barbaric = primitive:

For the members of the primitive household used to share commodities that were all their own, whereas on the contrary a group divided into several households participated also in a number of commodities belonging to their neighbors, according to their needs for which they were forced to make their interchanges by way of barter, as also many barbarian tribes do still; for such tribes do not go beyond exchanging actual commodities for actual commodities, for example giving and taking wine for corn, and so with the various other things of the sort.

Herodotus , another historian of the 5th century BCE (who, however, is as cross-cultural as anybody could be at the time, since he recognized many positive traits of other cultures and the Greek debt to them), assigns human sacrifice to the Thracians.^[1]

As Oeobazus was making his escape into Thrace, the Apsinthians of that country caught and sacrificed him in their customary manner to Plistorus the god of their land; as for his companions, they did away with them by other means.

Overview of Archaic & Classical Greek History by Thomas Martin, in Perseus:

16.2. Macedonians and Greeks

Macedonians had their own language related to Greek, but the aristocrats who dominated Macedonian society routinely learned to speak Greek because they admired the idea of being Greek and thought of themselves and indeed all Macedonians as Greek by blood. At the same time, Macedonians looked down on the Greeks to the south in Greece as a soft lot unequal to the adversities of life in Macedonia. The Greeks reciprocated this scorn. [Hdt. 5.20.4 ; Hdt. 5.22.1-2] The famed Athenian orator Demosthenes (384-322 B.C.) lambasted the Macedonian king Philip II (*359-336) as ``not only not a Greek nor related to the Greeks, but not even a barbarian from a land worth mentioning; no, he's a pestilence from Macedonia, a region where you can't even buy a slave worth his salt.'' Barbed verbal attacks like this one characterized Demosthenes's speeches on foreign and domestic policy to the Athenian assembly, where he consistently tried to convince his fellow Athenians to oppose Macedonian expansionism in Greece.

The following passage, also from Demosthenes, Philippic 3 31 [Dem. 9.31] , shows how certain religious festivals and institutions such as the oracle of Apollo were profoundly connected with what we might call the pride of being Hellenic:

Yet what is wanting to crown his insolence? Not content with the destruction of cities, is he not organizing the Pythian games^[2], the common festival of the Greeks, and if he cannot be present in person, sending his menials to act as stewards? [Is he not master of Thermopylae and the passes into Greece, holding those places with his garrisons and his mercenaries? Has he not the right of precedence at the Oracle, ousting us and the Thessalians and the Dorians and the rest of the Amphictyons from a privilege which not even all Greek states can claim?]

 Endnotes
[1]  On the Thracians, see, e.g.,Pausanias Description of Greece 9.30.5 [paus. 9.30.5]
[2]  Games in honor of Apollo at Delphi, the site of a great temple and oracle of this god, where not only Greeks but many foreigners congregated. This festival was similar to the ancient Olympic Games--though of lesser importance than the latter.