So a Human Walks into a Bar

I wrote the following story in the Eighth Grade for the regional Power of the Pen contest. We had 45 minutes and this was the prompt: Bees sting, roses have thorns; show what real---or imagined---defense system humans possess.

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"So a human walks into a bar," I said, leaning across the table to get a better view of my extraterrestrial companions.
"That is not funny," said Alien #1, whose name roughly translated to "Three Stalk Bison.
"I wasn't finished," I said testily. "Anyway, he walks into a bar...and falls unconscious. Why?" I looked at them expectantly.
"I have no idea," gurgled the gelatinous mass of bubbles, Alien # 2.
"Because---" I started, "he walked into a bar!"
No reaction.
"Into a bar, " I explained, and frowned. I was losing my audience. "You know, like that?" I made a rough gesture to hammer in my point.
"Don't humans have a defense system to prevent such...unfortunate accidents?" asked Mr. Bubbles.
I hung my head. "First of all, it's just a joke. You guys have no sense of humor."
Before Three Stalk could come back with a retort, I raised my voice to cut him off. "And secondly," I said, "humans do have a defense system. It's called embarrassment."
I received a quizzical expression from Three Stalk. "Embarrassment? Explain," he said, as if he was daring me.
"Well, see that guy over there with the four arms? Let's say he wants to ask that purple girl on a date," I hypothesized. "But he knows that if she turns him down, this will mean major embarrassment for him."
"But they are not humans," Mr. Bubbles pointed out.
I gave him a tight smile. "I'm just using them as examples, seeing as how I'm the only earthling in the bar."
Three Stalk wagged his finger at me. "But what about in a life or death struggle?" he asked.
"That too!" I exclaimed. "If you know you can't win a fight, you won't get into one. Because if you did, you'd be very embarrassed when you lost."
Mr. Bubbles chortled. "You'd be killed! That's what one would be afraid of!"
I shook my head. "If you're killed, that's a good thing! Then you won't be ashamed for the rest of your life!" I leaned back in my chair. "Having people snicker at you, that's what humans fear!"
"Your argument is confusing to us," Three Stalks said, although it was obvious he knew I had won.
"Confusing? It's easy!" I shouted. "As easy as why the chicken crossed the road!"
"Why?" asked Mr. Bubbles.
"To get to the other side!" I finished with a flourish.
No reaction.
"Aliens," I scoffed. "No sense of humor!"