What is the biggest lie you have ever told?

I was in choir once in 8th grade and one of the students was being loud and obnoxious. I loudly exclaimed "Would you shut the fuck up?!". Everyone stopped talking immediately. "Who said that?" Asked our choir director. "Will, did you just say that, or was it T. (the student who was being annoying)? If it was you, you should admit it and take the blame, but if it was T. I will take your word for it and punish him instead after class."

Now, because she had phrased it in such a clear dichotomous case study, it was clear that she knew very well I had done it. In fact everyone around me in the auditorium knew I had done it. T. was saying "It was him!", yet I was rather peeved that I was going to be held up as a moral exemplar by this woman because she assumed from my previous actions day-to-day that I was going to do the right thing and tell the truth, leaving T. unpunished but touching him deep within his heart with my honesty (yeah right), so instead in front of everyone who CLEARLY knew it was me I said it was T. who had cursed.

"All right", said the director with a manner of finality, "T. I will see you after class". After the session ended I walked the length of the far hallway for a minute and then came back to the auditorium to enter, confess, and take the punishment to allow T. to leave after "psyching him out", but I overheard the director talking to the pianist through the door before I entered: "NEVER before has a student lied to me like that right to my face. This is the first time. I am just shocked." She had let T. go already it seemed. Since he was free I had no reason to exonerate myself, her faith in her students not lying to her was highly misguided. She would think less of me for the next few years but perhaps also be more wary of miscreants in the future and stop trying to be so manipulative with the egregious social engineering. I walked away. It seemed we had both escaped.
　

BUT my love was in the room when this happened, so now this haunts me even though at the time I thought myself justified. A lie for the greater good of discipline and individualism is still a lie.