Head canon for this (ridiculously) short one-shot:
~France had feelings for Joan of Arc, and since she was burned at the stake by the English, it's a touchy subject for him.
That damn frog had done it again! France always knew how to push England's buttons, pissing him off immensely. At least my teeth aren't like a beggar's! He had spat at the Brit, who responded with a jab at his sixteen-year-old savior back in the Hundred Years War, Joan of Arc. France had stomped off.
England suddenly felt self-conscious about his teeth, running his tongue over them all through the World Meeting. It's that bloody stereotype! Not all English people have bad teeth! Even so, France's insult stuck with him.
When the meeting was over, England returned home with America, who immediately crashed on the couch. "Ugh, that was so boring! Nothing happened at all, how lame!" England simply nodded and went into the bathroom.
Staring at himself in the mirror, he bared his teeth. England had always thought they were fine before, but now he was concerned. What was it that people used to whiten their teeth? Salt? Yes, that was it, salt!
And since I'm England, if I have positively white teeth, my people's teeth will improve as well! With this resolution in mind, he dashed into the kitchen, pulled out the container of salt, and ran back to the bathroom.
"Is he gonna use that to cook or something?" America mumbled, very confused. He put a hand to his mouth in horror.
Loading the salt on his toothbrush, England began to scrub. His mouth started to ache, and then sting, but he kept brushing. He had to prove that frog-face wrong. He poured more of the condiment on his brush, and the cycle continued. When he felt satisfied, he finally spat into the sink and smiled at the mirror. That'll make France happy; they look like his stupid roses!
America burst into the bathroom, seemingly exhausted by running down the hall. Or perhaps he was breathing heavily simply for dramatic effect. No one will ever know. He grabbed the shorter man's shoulders. "Please tell me you're not gonna cook anything with that salt!" England thought of asking how, exactly, does one cook in a bathroom, but instead he shook his head. America heaved a sigh of relief and swooped in to kiss the Brit.
When America pulled away, a peculiar scent was on his lips. He licked them, and the sharp taste of iron filled his mouth. He looked at England, eyes wide. "England…?" He simply grinned, and what America saw was immediately branded in his mind.
Teeth colored red with blood.
Author's Note: Not all English people have bad teeth, okay? I live in America, and if you ever need some examples of bad teeth over here just come to my school. Most of them chew with their mouth open, too *shudders*.
So anyway, I was just thinking about how everyone assumes people from England and the rest of the UK have less-than-stellar teeth, and this popped up. Snapped! England, anyone?