HECTORI am unarm'd; forego this vantage, Greek.
ACHILLESStrike, fellows, strike; this is the man I seek. (5.8.9-10)
Moments after killing a Greek soldier for his shiny armor, Hector unarms and takes a break from battle. That's when Achilles shows up with his gang of Myrmidons. Everyone knows there's nothing honorable about killing a guy who's "unarm'd" on the battlefield, but Achilles doesn't actually care at this point. So, when Achilles goes after Hector here, it's the ultimate dishonorable action. But wait. It gets worse.
He's dead, and at the murtherer's horse's tail,
In beastly sort, dragg'd through the shameful field. (5.10.4-5)
After Hector is slaughtered, Achilles orders his body tied to a horse and dragged around the battlefield. This is majorly dishonorable, guys. Troilus uses the word "beastly" to describe what happens, although we don't think any animals could be so spiteful. Except maybe cats.