Women Happily Throwing Their Arms Back

There is no shortage of these types of photos on the internet.  I'm confused as to why this is the go-to pose, but I'm OK with it because they make me giggle. What is she so happy about? Or is she upset? It's hard to tell from this angle. I want to reach through the screen and ask her.

I think this lady's happy because she just bought this white bamboo jumpsuit for half-off at her favorite Hamptons boutique.