“[This is] an individual prayer for help against those who have slandered and falsely accused the one who prays.” (Psalm 140 footnote--NRSV Study Bible) If you take the time to read this entire Psalm, you find that the writer is very upset with their enemies, and wants God to do something about them.
All of us at one time or the other have felt exactly like this. No matter how much we pray, study the Bible, have reflection time, and try to love our neighbor, at some point in life we will be angry and ask God to do something. May you be able to make it through the anger you may have in your life and end up praising the Lord as the psalmist did. Vernon T.