Did you just call me "Dude"?

So yesterday I completely embarrassed myself. I was at school and our instructor gave us a break. He asked us if we wanted to get a snack from the instructors office. So several of us decided that we would go and get a snack....even though I am trying to not snack. So we were leaving the class room and the Sergeant made a comment and my response to him was "Dude......." I didn't even realize that I had called the Sergeant a "dude". So as I walk past him he says to me.."Did you just call me dude?" I was a bit dumb founded and speechless. I was so embarrassed. He wasn't mad and luckily I didn't get in trouble. But I did apologize in private later on that day because i felt so bad. He knew that i didn't do it on purpose....but still...a close call. had that been someone else, it could have been bad...whew!