From what I remember, there was a story where Pinkie Pie and Rainbow Dash were selling beverages that could cause ponies to outright lift off from farting, and after Spike consumed one, his butt incinerated Twilight, horrifying them, but then he revealed it's not the first time he's accidentally sent Twilight to Celestia.
I know it's not in this group's folders, and it might be somewhere on this site and I just can't find it.