Every organisation has a clear set of guidelines (Code of Conduct or other contract) that spells out exactly what's expected of every member, how they can be expected to be treated, and what to do when things go wrong. But this kind of agreement is lacking in our everyday lives. And without an agreed set of guidelines for social interaction, things can – and do – go in undesired directions.
We all know someone who gets a bit "handsy" when they've had a few.
We've all heard dodgy comments about another person's appearance / beliefs / gender.
We also know someone who can get a bit belligerent when drunk.
Yet when it happens, we tend to change the subject, brush it off, or find other ways not to address this kind of behaviour, because it makes us uncomfortable, we don't know what to do about it, or we don't want to spoil the vibe.
It's so much easier to be a bystander, but in doing so, we are giving tacit permission for this kind of thing to carry on, even though we don't agree with it.