sentence

Janice: Good Morning Joey!
Joey: Good Morning: ( said it in a dull way, as he was not in a good mood).
Janice: Oh, Today someone is wearing grumpy pants.

I don't get the meaning of the above sentence.

Thnx.

"Oh, today someone is wearing grumpy pants"="You are grumpy today"

It is an indirect and "funny" way of telling Joey that he seems grumpy, although instead of making Joey laugh, it will likely just make him more angry.