I went in search of a "facepalm" image (to include in a reply to someone posting about something stupid they had to deal with on ITFF and I found this. I think it's wonderful
It riffs on a famous Tommy Lee Jones facepalm picture that I won't post here as it contains a strong word I prefer not to use (and a term of insult that I would never use), but this version euphemises it nicely (and in keeping with Pony-speak). Also, Rarity's expression is very close to Jones' in the other picture.
This kind of thing just makes me smile. I think I may have to start using "so feathering derped" when something is really messed up.