James was pretending not to watch Lily. Lily was watching James pretending not to watch her. Sirius was watching James and Lily act completely ridiculous.
How could this have happened? He had been everything his mother had told him to be. He had obeyed every order. Somehow, it had to be his fault. It was always his fault... Marauder/MWPP-era, Sirius-centric.
Summary: An explanation in boggarts. This is all I have right now, but I'd be happy to write more if you want. Just let me know what characters you would like to see next.