Jesus, believe it. I actually had the chance to avert this before this started. He asked if I knew the password. I did and I told him, because I couldn't bring myself to lie.
Going behind his back? Totally different.
EDIT: On an unrelated note, in religion (AKA a subject I lost interest in last year and so far there's been no concrete evidence that interest is ever coming back), one side of the class was talking. The teacher, deciding to TAKE CHARGE (yes in all caps) made the entire class stop work and copy out a fairly info-heavy couple of pages in our text-books in ten minutes or we'd get detentions. This was in class, not in a detention, and we were specifically there to learn, not to fuck around by copying information that was right in front of us, for no discernible reason. I didn't finish, and I am not showing up for the detention, that's for fucking sure. If she wants to punish me for not wanting to not learn then she can go to hell and give them my regards when she gets there.
I plan to bring this up when she calls me out on not turning up for the detention. Hopefully this'll end in her feeling silly, but there's some magic power teachers have that let them ignore the facts and instead focus on the fact some punk kid's saying something out of line, so my chances don't look good.