One of my posts last summer about Virgil's Aeneid was about trash talking, and his Third Eclogue begins with a vigorous exchange of insults between Damoetas and Menalcas, before concluding with their singing competition, which their judge, Palaemon, ends up calling a draw. Here's a nice example of the trash, from Damoetas:

Maybe it was the day, right here, near these beeches,
When you broke Daphnis' bow and his arrows, too,
Because you couldn't stand the idea, you prick,
That that boy was given them as a song prize.
You were dying to get back at him.

As for me, I vote for Damoetas as the winner (which will of course lead Menalcas to shower me with insults), for this couplet:

Pollio loves my songs, however clumsy;
Muses, offer a calf to placate readers.

All this in David Ferry's translation, by the way.