The Apostle has been quite straight about the sort of behaviour that is off-limits for Christians.  It may jar with the tolerant age which has become usual in the West, but 'living in the light' will always be a peculiar lifestyle to those who don't love Jesus (1 Peter 4:4).  The 'deeds of darkness' are described as being 'fruitless' - they have no ability to produce any of the good things that God desires of us.  By contrast, when sin is brought to the light it can be dealt with in the same way that a surgeon can remove a cancerous tumour when it is visible through the illumination of the focussed lights in the operating theatre (1 Corinthians 5:12-13).

Christian fellowship is a special relationship in which we can call each other to account: and this is one of the reasons why the church home group, office Christian group or the work's prayer meeting is so important.  If one person goes off track, the others (in a spirit of gentleness - Galatians 6:1) should be there to help him or her be restored to fellowship and fruitfulness (James 5:19-20).  

Gossip is not caused by a loose tongue: it is fomented in a malignant heart.  The coffee room conversation that starts with, "Have you heard ...?" is the beginning of a reputation ruined or a friendship shattered.  Discussion of 'after the office party' is hardly ever profitable, and best left unsaid.  People will go wrong and mess up, but to perpetuate a moral superiority over them is hypocritical, and to recommend their behaviour as normal or exciting is perverse.  If anything has to be said it needs to be done with a heart full of love, because love covers over a multitude of sins (1 Peter 4:8).

Alas, many of our motives are mixed.  The problem with the mixed motives, that so easily spoil our lives, is that we justify joining in on the edge of dark things.  Yet when darkness overtakes another believer, an ugly censorious spirit rises up to blame and defame.  The cure for all this is to keep a keen eye on one's own heart.  Start by deciding not to speak about wicked things, look at wrong images, go to ungodly places or to keep serious company with those who will do their best to pull you into their muddy swamp. Although you may be ridiculed for refusing to join the darkness, they will eventually recognise that you were right before God (1 Peter 2:12) and be grateful that you were different.