Just last night I was in my office finishing a bowl and for some reason I started puffing rapidly, creating a wonderful thick dense smoke. I blew a dozen or more smoke rings for no particular reason at all. I saw this post and chuckled because I hadn't blew smoke rings in several months.
I do it, locopony, bu tI'm not super consistent with it. That's best indoors or really calm outside. The key is to fire out one really slow and then do the next with a bit more force, once the first one has spread out a bit. This guy closes the gap on his ring before blowing the second, but that's too mush walking around for me.
http://www.youtube.com/watch?v=QxITFHOIGRo