Hey Apple, What's So Dirty About My Gift Card Note?

Reader Sai says:

This is kind of weird: so, I’m trying to buy my friend an Apple gift card off of their website. My friend is pretty shy about celebrating her bday, so I wrote in the message that accompanies the card: “Happy birthday! I hope you aren’t shy to celebrate this year!” After I typed that, I got a message that deemed my message inappropriate?

Eh?

We couldn’t figure out what was wrong with it. Can you?