Teaching is the kind of thing which a lot of people consider to just be a profession, and not a fun thing at all. While you can be the kind of teacher who simply marches through their career with the stoicism of a soldier going off to war, you do not have to be this way if you do not want to be. After all, this is not supposed to be a battle, but a cooperative effort between a group of people who are out to help themselves to be more successful in this world. The name of the game is becoming more successful, and this can be very enjoyable for everyone involved in it.
Enjoying yourself while you teach your classes might at first sound like an oxymoron. After all, this is supposed to be work, and work in this society is not generally supposed to be enjoyable. But consider that not only is the work that you have decided to dedicate your life to doing, it is also work which involves young people. Young people are full of energy and life, and just being around them can be a lot of fun. At the very least, their high energy tends to be very contagious.
The energy of youth, coupled with the fact that at heart most young people actually do enjoy learning new things, is what makes teaching enjoyable. Granted, it is extremely hard work and the pay is not very good, to say nothing of the fact that a lot of students have been conditioned to hate the process that our society calls education. But when you get through that garbage, and really focus on doing something productive, it is quite enjoyable.