It's okay to encourage your friends to break out of their bad habits. You shouldn't be aggressive about it, obviously, but the better we are, the more God's light shines through us. It's okay to tell them they shouldn't swear, that they shouldn't use the Lord's name in vain, that they shouldn't be so mean. It's okay to correct them when they slip up. We should encourage each other to be the best we can for the Lord to shine his light through us!