II Thessalonians 3:14 And if anyone does not obey our word in this epistle, note that person and do not keep company with him, that he may be ashamed. 

Over my lifetime I've witnessed people I know, even friends, make poor choices that have resulted in broken marriages, loss of jobs, even brought through the court system and jailed. I've wanted to offer some encouragement to change their ways, and at times I've done that, but other times sat in silence. It pained me to see the brokenness from the fallout of their wrongdoing. 

Today's passage encourages us to be observant of others' misguided ways and put some distance between them and us to show our disapproval and bring them shame. If the opportunity presents itself, it's good to “speak up” and encourage them to turn from the doom they are headed towards. Praying for them is essential, because God is most likely working in their life, outside your view, to bring conviction and hopefully repentance. 

II Thessalonians 3:15 Yet do not count him as an enemy, but admonish him as a brother. 

God put people in our lives as friends, mentors, and spiritual guides, to help us navigate life. Although your acquaintance might be offending you by their actions, don't make them an enemy, but use this time to show them grace and mercy, through tough love and leave the rest up to God.