Is it right for a person to pray that God avenge him...

I would not say this is right or wrong, but a mistake. I say this because I aspire NOT to judge anyone. If we are to look at it from a religious point of view, is it not written that God is All things. He is in everything? Therefore to be part of the Whole he is going to be in each and everyone of us. Those who are cruel and hurt others, have merely lost sight of who they really are. Therefore judging and condemning them isn't going to resolve the issue. But that's what's been happening for thousands of years - wars, killing and so on. I am a Zen practitioner, and if I look at it from a Zen point of view, I aspire (through Zen meditation) to realise that I am at one with all there is. If I am asking for vengeance or pain in another, I am also attacking myself, because just by knowing that person, he/she has become part of me. So praying for something like that would be rather silly for me.

Please allow me to quote Matthew 5:38-48: "You have heard that it was said, 'Eye for eye, and tooth for tooth.' But I tell you, do not resist an evil person. If someone strikes you on the right cheek, turn to him the other also. And if someone wants to sue you and take your tunic, let him have your cloak as well. If someone forces you to go one mile, go with him two miles. Give to the one who asks you, and do not turn away from the one who wants to borrow from you. You have heard that it was said, 'Love your neighbor and hate your enemy.' But I tell you: Love your enemies and pray for those who persecute you, that you may be sons of your Father in heaven. He causes his sun to rise on the evil and the good, and sends rain on the righteous and the unrighteous. If you love those who love you, what reward will you get? Are not even the tax collectors doing that? And if you greet only your brothers, what are you doing more than others? Do not even pagans do that? Be perfect, therefore, as your heavenly Father is perfect," In my personal view, one of the reasons I believe in the Christian faith is that it tells us to do what is against our human nature. When bad things are done to us, the human instinct is to respond with evil, to attack, get back and take revenge. This is our natural response and the result is that evil triumphs. While they do evil to us, we want to retaliate to them. But Jesus tells us to act exactly contrary to our own nature, to respond to evil with good. Now this does not mean that wrongs are to be disregarded. This does not mean that people guilty of crimes are to let go. That would destabilize society, and what God wants to happen would fail. God established governments to uphold justice. "Do not resist an evil person" is the word of Jesus that we are never to take the law into our own hands, that we are not to take private vengeance. It is the government's responsibility to take action, not individuals. I Peter 2:13-14 (NIV): "Submit yourselves for the Lord's sake to every authority instituted among men: whether to the king, as the supreme authority, or to governors, who are sent by him to punish those who do wrong and to commend those who do right." Further the Bible says, "Do not repay anyone evil for evil. Be careful to do what is right in the eyes of everybody. If it is possible, as far as it depends on you, live at peace with everyone. Do not take revenge, my friends, but leave room for God's wrath, for it is written: "It is mine to avenge; I will repay," says the Lord. On the contrary: "If your enemy is hungry, feed him; if he is thirsty, give him something to drink. In doing this, you will heap burning coals on his head." Do not be overcome by evil, but overcome evil with good." (Romans 12:17-21). This is exactly what we should do. God calls us to do some painful, unnatural things. Keep on being faithful in the face of madness and the evil. Love your enemies. Pray for your persecutors. For in the end, we are unable to truly become like God on our own. But with God's help we can be at peace with God, at peace with ourselves, and while our world is still filled with violence and hate, with God's help we can be makers of peace.- Bible Commentary