It wasn't that she was a bad flier, exactly. Rainbow Dash, for instance, had a slightly worse crash rate than Ditzy. It was just that when Ditzy crashed, there was often collateral damage. Most other pegasi had the control to steer out of the way of buildings. And Ponyville, being founded by Earth ponies, was still a little biased against pegasi.
So it was completely natural that when the small town learnt that Ditzy 'Derpy Hooves' Doo had taken a job with the Royal Mail, a job that required extensive flight across town, that there was a little caution and skepticism amongst the ponies in town.
"No, really," said one earth pony, in hushed tones as the dawn broke over the small town, "she didn't look too good when I saw her this morning. Definitely more distracted than usual. She hit her mailbox when she left her house. Might be a good idea to keep a look out."
"You think? She's been getting better, though," said the other, also an earth pony. "She hasn't hit anything particularly dangerous in at least two months."
"Which means it's just about time that she did," said the first, "I'm just saying, keep an eye out, because you know, she's probably not going to be as attentive today. One good sudden breeze, and bang, she's through a window, or a wall..."
And because Ponyville has a rather vigorous gossip circle, the news that Ditzy Doo was not at her best quickly spread through the town. Everypony was looking up at the sky, watching for a careening grey and yellow pegasus. If the houses and market stalls had eyes, they would also probably be looking up. After all, Ditzy had crashed into a good number of them over the years since she'd moved to Ponyville.
The whole thing culminated at around lunchtime. Ponies were taking bites of their lunches, glancing up at the sky at every pegasus, or even at every sudden shift of the wind.
"What are we looking for?" asked one pony, as she sat down on the bench next to Lily.
"Ditzy Doo," said Lily, still looking up at the sky, "I've heard that she had a really bad night last night, so now she's all distracted, and I don't want to be in her way when she crashes today."
"Okay then," said Ditzy Doo, adjusting the bandages binding her left wing to her side. She'd misjudged a tree yesterday when completing her mail route, and broken her wing, and it was still healing. The doctor had cleared her to do her mail route, but she couldn't fly for a few days. Ditzy sat next to Lily for a few more moments while she finished her lunchtime muffin, courtesy of Pinkie Pie.
"You have a good day, Lily," said Ditzy, getting off the bench, tossing the paper wrapper in the bin.
"You too, Ditzy."
Ditzy grinned as she walked away from Lily while the flower seller realized what had just happened. The pegasus was rewarded with the earth pony bolting past her, screaming, not two seconds later.