I struggle to bless nasty people! Will they take advantage of me if I do?
You are right that it is difficult to bless nasty people. Our natural response is to hate those who make life difficult for us, and to fight back when we are attacked. However, the Bible tells us that this is the way the world around us works, and God has called us to live in a different way.
Not only does Romans 12:4 tell us to “Bless those who persecute you: bless and do not curse”, but in Matthew 5:44 Jesus tells us to “love your enemies and pray for those who persecute you”, and in Luke 6:27 to “love your enemies and do good to those who hate you”.
Christians should be different from the world around them because they know and love Jesus, and Jesus asks us to love other people no matter what they do to us. Paul tells us that when we are cursed, we bless; when we are persecuted, we endure it; when we are slandered, we answer kindly (1 Corinthians 4:12-13). We cannot do this on our own, but we ask the Holy Spirit to help us to respond in the right way.
Other people cannot take advantage of us when we live like this because God promises to be with us when we live in obedience to Him (Amos 5:14, Philippians 4:9). When God is with us, there is no-one who can stand against us (Psalm 56:4, 118:6, Romans 8:31). We are never put to shame when we trust God and do things His way (Psalm 71:1).
It is difficult to bless people who are nasty towards us, but God has clearly told us the way He wants us to live and He has promised to be with us when we obey His word.