I couldn't train without smiling and having fun but then again I don't consider myself a teacher or martial artist..

I am a former fighter and fight coach.. I try and have fun and train hard but joke around while doing it.. This is a voluntary endeavor that should enhance your life not bring stress to it. I train, joke and have fun

Hell when I compete I smile, joke around and have fun

You have a very strange concept of judokas. I've been doing judo for over 60 years, and there's never been a class where folks weren't smiling or laughing at some point. Judo brings out comraderie (as does most martial arts) and helping and enjoying each other is a big part of jita kyeoi (mutual benefit).

When I was in high school, one of the history profs stopped me on the stairway and told me "You smile too much". That summer I took his American history class (so I could have extra time slots for A.P. courses in my senior year. He turned out to be one of the best teachers I've ever had. But he was also one of the biggest cynics I've ever encountered. (Probably because he was a history professor.)

if bjj wasn't fun I wouldn't do it. Laugh and smile all you want.