Just like you HH, my parents always took the side of authorities, teachers, other parents when I pulled dumb stunts. It sure pissed me off then and I always thought they were against me. Reminiscing about those times, my parents now see it my way!!! GRRR hahaha. "WHAT!! you actually thought the teacher was WRONG?? " They provided me with unconditional love and a sense of civility that I am now grateful for. Parents should be parents not friends and enablers. Kids will grow and appreciate good parenting.
EDIT: Splashopper, I think what you did was ok. You're not the parent or the kid so your not to blame for anything. If the dad hates you after this, then nuts to him.