Does this make me a jerk?

I am a nice person most of the time - really I am. Unless I get cut off in traffic or someone tries to harm me or my family I will be calm and pleasant. This story takes place 02/19/09 at the milk & sugar-adding-area of my local coffee place and because I use fake names on my blog the codename will be 'Moonbucks'.

I was waiting patiently for the person before me to finish adding her milk so that I could go next. I was listening to death metal in my right ear so when she asked me something and gestured towards the dairy offerings I couldn't hear exactly what she said. I mumbled an inquisitive "hmm"? this caused her to gesture angrily at the dairy options. I displayed a confused look which made her throw up her hands and walk away muttering something about "kids these days". I am 33 years old, granted a very immature 33 but calling me a kid gave me the justification to then say "I can get my own milk" - I don't know if she heard me or not.

I don't know why she couldn't just be like everyone else and leave when she was finished adding milk to her coffee. There are so many jerks in the world that it throws me off when someone is genuinely trying to be helpful. The song I was listening to is "Scavenger of human sorrow" by the band 'DEATH'.