It's not very common and typically it would be used to make light of the fact that someone is the odd man out. It could be used where others are aware of something and you weren't. (Miley Cyrus lyrics in Party in the USA) Or it could be used for a coincidence. (I meet a bunch of friends that I haven't seen for years and they all have beards and I don't.)

“Didn’t get the memo” - To be or to remain uninformed, especially about something that is common knowledge to everyone else but you. Ex: Everybody seems to be wearing green today - I guess I didn't get the memo. Hope it helps!

It's an uncommon expression where I am. You use the expression (I didn't get the memo) when you thought you should have been told of something and you weren't, OR, you had no idea about something but someone else expected that you knew. Example: A: "Why weren't you at the meeting ? You were expected there." B: "I didn't get the memo - I knew nothing about it"

Thank you so much!

Memo essentially means message. So, "not getting the memo" means you were not told/unaware of. It is often used in joking situations. eg. Everyone wears pink except you. "Oh wow, nice outfits, I didn't get the memo." It is not very common in Australia, but still used.