What's so funny?

Xiao walks over to you, drinking a can of soda. You both were in the middle of filming for an upcoming movie, and it was break time. Obviously you'll use your phone so you won't get bored, and you wanted to talk with someone to pass the time.

You didn't even notice you were laughing, not until your on-screen partner, Xiao, pointed it out. He was frowning. Why's he so upset?

Who are you talking to?