King Pyrrhus of Epirus (318-272 B.C.) wrote himself into common speech by winning such costly battles against the Romans in southern Italy that the term Pyrrhic victory was coined after him: "One more victory like this, and we're lost."

However, less renowned are the events leading up to Pyrrhus' involvement in Italy: Of how the rich Greek colony city Tarentum, with its fleet the strongest in all of Italy, signed a treaty with Rome that forbade them entering the Bay of Tarentum. Of how a Roman flotilla broke this treaty, and then was ruthlessly attacked by the angered Tarentines. And of the failed Roman embassy to Tarentum, which ended in disgrace and a declaration of war, whereupon the Tarentines realized that entering into war with the strongest power on land in all of Italy without allies backing them was a horrible idea. Which in turn led them to invite Pyrrhus, who rapidly took full control of Tarentum and drilled its young men for war, much to the Tarentines' dismay.

As Polybius gives us the flavour of, this was an age boiling with war at every side (my italics):

Quote Originally Posted by Polybius
First, by dint of valour, and the good fortune which attended [the Romans] in the field, they mastered all the Latini; then they went to war with the Etruscans; then with the Celts; and next with the Samnites, who lived on the eastern and northern frontiers of Latium. Some time after this the Tarentines insulted the ambassadors of Rome, and, in fear of the consequences, invited and obtained the assistance of Pyrrhus. [B. C. 280.] This happened in the year before the Gauls invaded Greece, some of whom perished near Delphi, while others crossed into Asia.
Now this particular incident of shaming the ambassadors of Rome is a gutsy one. One deserving of wider fame.

Enter, the work of Appian of Alexandria, whose writings survive as fragments in Byzantine tomes. Pay special attention to part 16:

Quote Originally Posted by Appian
[15] [From Constantine Porphyrogenitus, The Embassies] Cornelius went sight-seeing along the coast of Magna Graecia with ten ships with decks. [283 BCE.] At Tarentum there was a demagogue named Philocharis, a man of obscene life, who was for that reason nicknamed Thais. He reminded the Tarentines of an old treaty by which the Romans had bound themselves not to sail beyond the promontory of Lacinium. By his passion he persuaded them to excitement against Cornelius, and they sunk four of his ships and seized one of them with all on board. They accused the Thurini of preferring the Romans to the Tarentines although they were Greeks, and held them chiefly to blame for the Romans overpassing the limits. Then they expelled the noblest citizens of Thurii, sacked the city, and dismissed the Roman garrison that was stationed there under a treaty.

[16] [From Constantine Porphyrogenitus, The Embassies] When the Romans learned of these events, [282 BCE.] they sent an embassy to Tarentum to demand that the prisoners who had been taken, not in war, but as mere sight-seers, should be surrendered; that the citizens of Thurii who had been expelled should be brought back to their homes; that the property that had been plundered, or the value of what had been lost, should be restored; and finally, that they should surrender the authors of these crimes, if they wished to continue on good terms with the Romans.

The Tarentines made difficulties about admitting the embassy to their council at all, and when they had received them jeered at them because they did not speak Greek perfectly, and made fun of their togas and of the purple stripe on them. But a certain Philonides, a fellow fond of jest and ribaldry, going up to Postumius, the chief of the embassy, turned his back to him, drew up his dress and polluted him with filth.

This spectacle was received with laughter by the bystanders. Postumius, holding out his soiled garment, said: "You will wash out this defilement with plenty of blood - you who take pleasure in this kind of jokes." As the Tarentines made no sort of answer the embassy departed. Postumius carried the soiled garment just as it was, and showed it to the Romans.

[17] [From Constantine Porphyrogenitus, The Embassies] The people, deeply incensed, sent orders to Aemilius, [Consul Lucius Aemilius Barbula; 281 BCE.] who was waging war against the Samnites, to suspend operations for the present and invade the territory of the Tarentines, and offer them the same terms that the late embassy had proposed, and if they did not agree, to wage war against them with all his might. He made them the offer accordingly. This time they did not laugh for they saw the army. They were about equally divided in opinion until one of their number said to them as they doubted and disputed: "To surrender citizens is the act of a people already enslaved, yet to fight without allies is hazardous. If we wish to defend our liberty stoutly and to fight on equal terms, let us call on Pyrrhus, king of Epirus, and designate him the leader of this war." This was done.
Now, anyone up for a fantasy diorama based based upon the exploits of Philonides of Tarentum? Or a 40k version, for that matter, given Ian Watson's textual corpus in this setting? :P