Background: Its seems like this girl is interested in me, we've been friends for a while and she likes to flirt sometimes. Sometimes i jokingly hit her if she gets "out of hand"

In class i would make mean and funny comments, half the times she likes them but she would be like: omg youre so mean, go kill yourself.. or something similar, granted she wouldnt want me to hurt myself in any way. Also i gave a mean nickname to this guy in our PHI class for talking too much, and started calling my friend that, when she spoke too much. I know shes kidding but she would call me "ugly" as a nickname.

How do i respond to these??? Each instance only happened once, so its not like its constant "harassment"