Yes, you're right. You have to do this well. I ended up having a great relationship with my students that year. But I think my principal had to field calls from confused parents.
Right, you wouldn't want to betray their trust. However, my personality and teaching style led me to "pull their leg" every so often which I think is quite age-appropriate for 8th-graders. That's right at the age where the brain is developing new types of abstract thinking, and so the occasional tongue-in-cheek communication really exercises their brain well and if done well can establish a playful rapport with the students. I found that this doesn't work with 6th-graders, though. They are still rather concrete in their thinking.