Fire

Hey you, mother of a very sick toddler, why not stay home or use a car instead of bringing your coughing, gurgling, snotty kid on a full train of people who do not want to get sick. 

Seriously, lady. Your kid is openly coughing vertically from her chair into the air. From across the train I can see the virulent mist cloud rise from your little baby's lungs and hover and dissipate.

The baby didn't drive to the train station and choose to ride the train. And she is too young to know how to cover her cough. She is just a cute little innocent Patient Zero.

You, however, do know better. Therefore you are who I want to neck punch right now.