Depending on how you did the lesson of course. I could see it as valuable if you were asking the students to explain why your observations don't fit with the actual world.
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.
Indeed, I see this as a kind of QA for science education. If you can trick your students into believe unscientific bullshit then you've failed to teach them science.
> "Your job, as students, among other things, is to try and catch me in the Lie of the Day."
Except this is very often going to be exactly what you are doing. Take nearly any scientific subject you had in school. How much of what you learned still holds? Not to even mention that the text books the children are reading often contain information that has already been disproven.
Heaven forbid (pardon the expression) they stop automatically trusting everything anyone in a position of authority says to them, and start keeping an eye out for bullshit and/or forming their own opinions. Won't somebody please think of the churches!