I'm going to argue with a pregnant woman who is serving me at a restaurant
What made you want to argue with her?
She gave me a dirty look.
She may not have intended to give you a mean look so it would be rude to mistreat her based on that alone. Giving her a bad time may make your experience worse than it already is.
No, I can read her mind. She gave me a look of disgust and I'm going to call her out for it.
I highly doubt she did. There are so many people she needs to watch in the restaurant, you can't blame her for making a face especially because you don't know who it was for.