Working in customer service requires a certain level of tact. A poker face is required. 

When dealing with people all the time and you need to be nice, gracious, curtuous, sometime you need to down right think of something else to keep a straight face and not burst out laughing. 

Poker face isn’t just for the customers, it applies to Co-workers too. It’s hard. Especially when people aren’t innocent and aren’t the nicest of people a poker face is necessary.

I’ve always been bad at a poker face, I’m getting better at it but it’s difficult. It’s necessary in this world but so hard.