I would only tell if a neighbour was having a party with people coming and going all the time. This is highly unlikely because I live in a quiet road with mainly elderly neighbours or young neighbours with young children (who buy the houses when the oldies start disappearing).
There is no way I would report a neighbour that had more than 6 people in total paying a visit. I am not going to sit behind my twitchy curtains counting the people in.
Royal Dress Code in Hot Weather


