I don’t know what The Truth is, but I do know that I’m with truthsharer on this one, and it has been a little startling for me for a long time.
It’s a bit of a stretch to compare a Rav saying something jokingly to a forum full of mixed ages joking with each other. Try a more comparable situation: imagine a scenario in which your husband brought home a few friends/chavrusas one evening. Imagine you coming in to the kitchen and chatting away with them, pulling up a chair and enjoying the camaraderie, and throwing in some good well-timed jokes and making everyone laugh. From the way you described your husband, I think he would turn colors. Imagine a couple of your friends happened to come in at that time, and you all sat around the table enjoying a good shmooze. That may be fine in some circles, and it is not my place to judge or to determine if something is tznius or not. But from the way you describe yourself and your husband, it seems quite inconsistent.
A lot of people make this mistake, and think the internet gives carte blanche for all things considered highly inappropriate for their own everyday behavior, so long at it is “anonymous”. As long as someone has identified themselves by gender (sorry haifagirl :)) either through screen name or through blog content, the scenario is not far from the one I painted in your kitchen. There are real live people behind each screen name.
Again, I am not judging one’s personal tznius standards, do not give mussar on this topic- I’ve got loads to do on my own before I can turn around and offer criticism to the next person. It still remains that truthsharer assessment seems to me to be accurate, and those who don’t flirt/trade jokes (really, dictionaries don’t do justice to the everyday connotations of some words/actions) in person should realize that it’s much the same on the internet. I’m sure I can look back and find instances of where I’ve done this myself, I’m the last person to judge.