Herodias gets even

Mat 14:6 But when Herod's birthday was kept, the daughter of Herodias danced before them, and pleased Herod.
Mat 14:7 Whereupon he promised with an oath to give her whatsoever she would ask.  

Mat 14:8 And she, being before instructed of her mother, said, Give me here John Baptist's head in a charger.
Mat 14:9 And the king was sorry: nevertheless for the oath's sake, and them which sat with him at meat, he commanded it to be given her.
Mat 14:10 And he sent, and beheaded John in the prison.
Mat 14:11 And his head was brought in a charger, and given to the damsel: and she brought it to her mother.

Why was Herodias so angry at John?

Mar 6:17 For Herod himself had sent forth and laid hold upon John, and bound him in prison for Herodias' sake, his brother Philip's wife: for he had married her.
Mar 6:18 For John had said unto Herod, It is not lawful for thee to have thy brother's wife.
Mar 6:19 Therefore Herodias had a quarrel against him, and would have killed him; but she could not:
Mar 6:20 For Herod feared John, knowing that he was a just man and an holy, and observed him; and when he heard him, he did many things, and heard him gladly.

A prophet speaks the word of God with power, not with words of sugar, but to the point. When we witness we are to speak truth with grace, but a prophet just gets to the message; John had to speak the truth. Herodias, having married the governor thought she was above criticism. She had power in her position and was only angered, wanting to remove the opposing viewpoint, by killing John. Ruthless people like some politicians will remove opposition, even by murder to keep their power and their way of believing.

At the birthday party, Herod was distracted and perhaps drunken. The devil looks for opportunities to take over and will entice and then sneak in his deathly will. Perhaps Herod was lusting after the daughter of Herodias making an unconditional oath to give her anything that she wanted. Herodias used this opportunity to kill John the Baptist because of her anger. Anger towards someone who speeks the truth is the wrong response. A more appropriate response would be guilt and repentance. 

I knew a Christian man who divorced his wife and married her pretty sister. Both were divorced and they married each other. The man never again attended church, he seemed to be cut off spiritually. Is there any sin that Jesus cannot forgive? Conviction and repentance, turning to God and seeking forgiveness is the correct response to sin; as David did after sinning with Bathsheba. He was restored, but his actions had consequences, for his family was troubled. Sin has a harvest, but Jesus is Lord over the harvest as well. Always come to him to be restored and put away anger. Is there anyone's head that you want brought to you? Anger kills so put it away and seek forgiveness. Seek life and truth not death and destruction. Learn forgiveness and walk in God's love.