A canine great unknown line

I haven't published one in a little while and there was one that I remembered. I wanted to save it while I had it in mind. It dates from my early days when I was working in a school. I was still enthusiastic about this new job that was paying badly, as I thought it could lead to more and I was not yet treated like dirt by some of the staff. And I was also a novelty for the pupils, so I was interesting to them as a newcomer. Before class, some of the girls, among the naughty ones, sometimes trouble makers, were chatting. I had been warned about them right before they moved in. One asked me my age, I answered 30, and the leader of the group said: "That is 140 in dogs age, sir." I answered: "Well, it's a chance I am not a dog." She started laughing and was still laughing at the joke when the course started. I had many difficult classes and many difficult moments there, but ironically enough, never from this class and never from these girls. I often wonder if it was not because of that throwaway line.