How do I react?

It was really hard to even think of a title for this because I'm so confused by this, okay now for the story. I was in a line to get something in one of my classes, and for context I usually stand a little to the side when in lines to see how much longer thr line is, so I was going into the line and I walked a little to far forward almost going in front of the girl in front of me, so this girl and I don't really talk to each other much but every now and then we will and we are usually friendly, so I accidentally walked to far in front of as previously said and then she turned, put her hand directly in the middle of my chest and jokingly said stuff like "you better back off buddy" and stuff like that while making direct eye contact and said like 3 things like that then just looked at me for a second longer and stopped talking then turned around and did a little laugh. what was I supposed to do, how do I respond to that, I was so confused and still am