I make a very serious disclaimer about school appropriate conversations. I use the teacher view to immediately call out anyone who is inappropriate. It reinforces the concept that someone is or could be monitoring all internet traffic. I make a screen shot of any offensive chatter and have an 1-on-1 with the involved students. It is also an opportunity to talk about Internet safety and free speech.
For the back and forth, conversations I used corny jokes specifically knock-knock jokes.