The term facepalmsunday was probably first used in this meaning in this Twitter message during the vote counting: https://twitter.com/#!/yousifabdullah/status/59702195561570305 The origin as a Twitter hashtag contributes to the fact that the word is written as a compound word, as opposed to two words "facepalm Sunday", because hashtags cannot contain spaces. Also, Palm Sunday is properly written as a compound word "palmusunnuntai" in Finnish.
2. Urgent/last minute grocery shopping (usually sunday) only arriving seconds before the shop/store is about to or has closed for the day
3. Waking up on a sunday morning after a "heavy" weekend (Friday and Saturday) of binge drinking/drug taking with a massive hangover/headache and unknown partner/s (usually sexual) beside you that you don't remember anything or who they are but are dreading the aftermath of what happened.
4. The one day or days of the year that Jesus (christianity), God or any saints and/or deities look down onto the Earth from their place of residence and cringe/express disbelief, shame or disgust towards humanity's frequent acts of stupidity
5. Fusion/combination of "Facepalm" & "Palm sunday"
2) man arrives at a supermarket only to see the front doors closed, looking to the manage who just locked the doors, the manager shakes his head and points to the list of clearly visible opening hours
Man: *moans* OH YOU HAVE GOT TO BE JOKING!
Store manager shakes his head
Man reads the sign indicating store opening hours, sighs and facepalms at his own lazyness/stupidity for not reading the opening hours - facepalm sunday momment