These funny birthday memes will do the trick ... of these pop-up birthday cards and stick it in the mail for a sweet surprise.

While celebrating her 31st birthday, Demi Lovato took a moment to have the last laugh over a meme that has followed ... one of which bore a fun surprise. "So I just want to show you guys ...

And funny birthday memes are pretty much guaranteed to put ... pop-up birthday cards and stick it in the mail for a sweet ...