What Kind Of An Insult Is "Chump Jaw"?

So I'm watching the old G.I. Joe cartoons and destroying my happy memories of them by finding out how terrible they really were. Here's a few quotes from the five-part "Revenge of Cobra."

• "I am a man with a big green thumb and I'm going to stick that thumb right in Cobra's nose."
• "Stop sputtering like a wet toaster."
• "This place has more twists than a pretzel factory with the bends."
• "This place is shaking like a ten cent milkshake."
• "We're going to get cooked like chickens!" "This is one chicken who plans to be gone long before then."
• "And I'm talking dead with a very big D".
• "Diamonds are a guy's best friend." "But time is nobodys friend."
• "Wrong again, chump jaw."
• "You're almost a sight for sore eyes." (I love how he said "almost.")
• "Snake is sneak spelled sideways."
• "Two's company, but three's a regiment."
• "I feel another presence." "That presence feels you as well."

Also, I kept noticing that they yelled their battle cry, "Yo Joe!" quite often so of course I had to count. In one 30 minute episode, I heard it 12 times. If you allow for commercials, that's about once every 2 minutes. On the other hand, Cobra only yelled 4 times. No wonder they never win.