Saying negative things about the people you are praying for is praying in unbelief. Are you not to pray for all people? If you are praying for them, then you are holding them up to your Father. It is hard to speak ill of someone for whom you are praying. True intercessors have let go of sniping words. Pray for people who get under your skin, until you are comfortable with having them there. Talk to your Father about them. See the good. Ask for grace for them and for yourself. When you pray for them, it will keep your words in check.
“As for me, far be it from me that I should sin against the LORD by failing to pray for you” 1 Samuel 12:23a (NIV)