Vs. 78 — Let the proud be ashamed, For they treated me wrongfully with falsehood; But I will meditate on Your precepts.

Thomas Manton:

When the proud are troublesome and injurious to God’s people the saints may boldly commend their cause to God.… The Lord may be appealed unto upon a double account; partly, as he is an enemy to the proud, and as a friend to the humble (James 4:6; Ps. 138:6); partly, as he is the portion of the afflicted and oppressed (Ps. 140:12). When Satan stirreth up his instruments to hate those whom the Lord loveth, the Lord will stir up his power to help and defend them.

Is not this a revengeful prayer?   Answer, No.

1st. Because those who pray it are seeking their own deliverance, that they may more freely serve God by consequence. Indeed, by God’s showing mercy to his people, the pride of wicked ones is suppressed (verse 134); but mercy is the main object of the prayer.
2ndly. As it concerneth his enemies, he expresseth it in mild terms—that they may “be ashamed”; that is, disappointed, in their counsels, hopes, machinations, and endeavours. And therefore it is not against the persons of his enemies, but their plots and enterprises. In such cases shame and disappointment may even do them good. They think to bring in the total suppression of God’s people, but that would harden them in their sins; therefore God’s people desire that he would not let their innocency be trampled upon, but disappoint their adversaries, that the proud may be ashamed in the failing of their attempts. (Manton, Thomas. The Complete Works of Thomas Manton. Vol. 7. London: James Nisbet & Co., 1872.)

Prayer:

Let the proud be ashamed, for they treated me wrongfully with falsehood; but I will meditate on Your precepts. Help me to keep my eyes upon You and Your ways, that is, Your promises. Do not let the words and works of the proud manipulate me to react to their falsehoods and arrogance. I do not want to be drawn in to their ways. Capture my attention, O’ Lord, and hold it steadfastly on Thee.  I do not pray that You would destroy those who speak against me, for they do not know what they are doing. They are blind and by nature children of disobedience. But I ask that You remove the veil that blinds their eyes from the Gospel, and that You would shine the glorious light of the Gospel of Jesus Christ into their hearts. Father, if it be Your will, let this circumstance against me, which is really against You, be a divine appointment for shame to bring the proud to repentance. May the harm which evil has devised be turned and to the saving of a soul–from the kingdom of darkness to the kingdom of light. Glorify Your name, O’ God!