Last night I went for a walk with DP before bed. A couple of blocks away from our house, we walked past a driveway with a car whose headlights were on. The garage was all locked up, the porch light off, and we could see people moving around in an upstairs room behind a curtain. It seemed pretty clear that they'd come home and forgotten to turn the headlights off, and would have a flat battery in the morning.
I said to DP, 'I'll just go and knock and tell them, shall I?' I mean, it's basic neighbourliness, right? I could see they were still up, I wasn't waking them.
DP was horrified. He found it really weird, interfering, and (I gather) Essentially UnBritish. AIBU to think it is normal and friendly, or would you be annoyed/ freaked out if a stranger knocked on your door to tell you this?