[KRX]

After rewatching "Hurricane Fluttershy," I don't think Flitter and Cloudchaser were actually laughing at Fluttershy, but rather Fluttershy flew by at a moment where they happened to be laughing, and her mental trauma made her perceive it as she was being laughed at.

UPDATE: I went back and rewatched the scene a few times. They do seem to be laughing at her, as indicated by Flitter pointing her hoof at Fluttershy while laughing. On the other hand, before Fluttershy flew by, the duo were looking at each other and smiling, and the pointing of the hoof later turned into Flitter wrapping a hoof around Cloudchaser, so they might have been laughing at a really funny joke.

At the very least, they might have redeemed themselves by complimenting Fluttershy at the end of the episode.