The Athenians defeated the Boeotians in 507 BCE after over a decade of an alliance with the Plataeans (also Boeotians). This was the beginning of over a century of trouble between the two cities, marked by Theban submission to Persia in 479 BCE. The Athenians set up an inscription to mark their victory:

IG I3 501 Dedicatory Inscription on the Acropolis after the defeat of the Boiotians and Chalkidians: cf. Herodotus 5.77 for a quotation of it:

“Sons of the Athenians with iron bonds extinguished
Their pride with their deeds in war
When they subdued the Boiotian and Chalkidian peoples
And then dedicated these horses as a tithe for Pallas Athena.”

[δεσμοῖ ἐν ἀχνύεντι(?) σιδερέοι ἔσβεσαν ῾ύβ]ριν
παῖδε[ς ᾿Αθεναίον ἔργμασιν ἐμ πολέμο]
[ἔθνεα Βοιοτôν καὶ Χαλκιδέον δαμάσαντες]
/ τôν Jίππος δ̣[εκάτεν Παλλάδι τάσδ’ ἔθεσαν

For the rest of the century, they had many unkind things to say about their neighbors to the north.

Aristotle, Rhetoric 1407a

“And Perikles compared the Samians to children because, while they accept the vote, they cry about it. The Boiotians, he claimed, were most like oak trees: since oak trees knock against each other and break and the Boiotians were always fighting one another.”

καὶ ἡ Περικλέους εἰς Σαμίους, ἐοικέναι αὐτοὺς τοῖς παιδίοις ἃ τὸν ψωμὸν δέχεται μέν, κλαίοντα δέ, καὶ εἰς Βοιωτούς, ὅτι ὅμοιοι τοῖς πρίνοις· τούς τε γὰρ πρίνους ὑφ’ αὑτῶν κατακόπτεσθαι, καὶ τοὺς Βοιωτοὺς πρὸς ἀλλήλους μαχομένους.

 

And a scholiast to Pindar reports why the epinician poet was worried about being called a pig (Schol. In Pind. Ol. 6.90):

“If we avoid the insult ‘Boiotian pig”: He uses this because the Boiotians were called ‘pigs’ due to their ancient rustic and vulgar nature. Pindar also refers to this in his dithryambs when he writes “there was a time when the Boiotian tribe was called “piggy” “. Kratinos, the comedian adds, These men are “Swine-men”….”

“εἰ φεύγομεν, Βοιωτίαν ὗν”: ὅτι διὰ τὴν ἀγροικίαν καὶ τὴν ἀναγωγίαν τὸ παλαιὸν οἱ Βοιωτοὶ ὗες ἐκαλοῦντο· καθάπερ καὶ αὐτὸς ἐν τοῖς διθυράμβοις (fr. 83)
ἦν ὅτε σύας τὸ Βοιώτιον ἔθνος ἔλεγον. καὶ Κρατῖνος (fr. 310 K.)· οὗτοι δ’ εἰσὶν Συοβοιωτοὶ, κρουπεζοφόρον γένος ἀνδρῶν.