parents, please - a few small things that you really need never mention at parent/teacher conferences:

Your child often reads the books I've lent him while sitting on the toilet.

The whens and whys and hows of your divorce

Your child's former best friend (and my current student) has recently turned into a total hussy and will sleep with almost anyone.

You think that reading is a silly waste of time.

Let's just say you wouldn't be opposed to the idea of trading money and/or goods for an A in my class.

Your recent graduate is adjusting quite nicely to college, and applying those hard-earned English skills honed at ___ High School by writing and selling essays to her friends for $50 a pop. 

You think all elective courses - regardless of what they are - are silly, unimportant "blow-offs," and the fact that your child is not earning an A in one means that the teacher is "ridiculous."   (I'd particularly recommend you avoid saying this if the teacher to whom you are venting happens to also teach elective courses.)

The particulars of your child's fairly benign, yet still sort of gross medical condition

That your child thinks I'm cute

That you think I'm cute

Thank you.  That is all.