I'm no expert on South Park. Rarely watch it, but it is quite funny.
In the case of the teacher, what I find especially funny is that the children don't seem bothered at all.
Reminds me of an episode where they tried a take off of Lord of the Rings, with, I think Cartman, playing Gandalf and the sensitive boy, (is it Butters?), playing Gollum. The adults became convinced kids had actually seen a porno movie and rushed to explain sex to them. The look on those kids faces should have been framed.