Psalm 12:4 describes the arrogant and boastful speech of the wicked. Let's break down the meaning:

"Who have said, 'With our tongue we will prevail.'" This indicates a belief in the power of their own words. They believe they can manipulate, deceive, and dominate others through their speech. They think their eloquence and cunning will always win. They see their tongue as a weapon to get what they want. "Prevail" implies a sense of victory, conquest, and control achieved through their speech.

"Our lips are our own." This expresses a sense of radical independence and autonomy. They believe they have the right to say whatever they want without any accountability to God or other people. It's a declaration of self-ownership and a rejection of any authority over their speech.

"Who is lord over us?" This is the defiant and rebellious core of their attitude. They reject the idea that God is their Lord and that they are accountable to Him. It signifies a complete rejection of divine authority and a claim of absolute self-governance. They deny any higher power has the right to tell them what to say or how to live.

In essence, the verse paints a picture of people who:

Are confident in their ability to manipulate and control others through their words.
Believe they are free to say whatever they want without any moral or ethical constraints.
Reject the authority of God and declare themselves their own masters.

The implication of this verse within the broader context of Psalm 12 is that:

Such arrogance and disregard for truth and righteousness are a source of corruption in society.
God will ultimately judge and humble those who use their words in this way.
The righteous can trust in God's faithfulness and protection in the face of such wickedness.

This verse highlights the destructive power of unchecked pride and the importance of using our words responsibly and in accordance with God's will.