No, this is not a joke. That is really the way the train attendant in the photo above is being
trained to hold a better, sweeter smile. It appears this type of smile training is standard practice in Chinese service industries because here is another photo of air force flight attendants in training, also with teeth clamped around a single wooden chopstick.
Looks like the stuff of Amy Chua if you ask me.

Girl puts three guys on a leash and takes them out for a walk

