I heard a teaching once that "INTEGRITY" is what you do when no one is looking. That proves that integrity is a heart issue. Often times I make the decision to walk in integrity. Be the bigger person, act like Jesus, be holier, ooze God's grace. But what I am really exercising is OUTegrity. I am going through motions because it is what I "should" do. In the recesses of my heart though I am fighting my flesh.
I am pretty sure in those moments where I "faked it", I neglected to ask God to forgive my attitude. I wanted Him to bless my actions. Some examples would be bitterness or my judgmental/critical attitude or whatever was on my "emotional menu" at the time. I have "acted"(and still do at times...insert friends nodding their heads here) like I am fine with a situation when I really am not. I confess I "chose" to take the high rode when in my heart and head I was kicking and screaming the entire way.
Let's face it. When you are "faking it" you become more resentful if you don't bring it to God to be dealt with. Luke 6:45 says, "The good man brings good things out of the good stored up in his heart, and the evil man brings evil things out of the evil stored up in his heart. For out of the overflow of his heart his mouth speaks."
We need to work out the issues of the heart so that our mouth will speak good things and that we really mean the good things we say. Words that are edifying and encouraging. Words that build each other up not tear each other down. Words that heal not hurt.
God gave us His grace. In turn we are to extend it to others. If we are "stuck" and we find ourselves "faking it" we aren't fooling God. Use Matthew 18 as a directive if you have been hurt or offended. If that is not possible then forgive as you have been forgiven. (It could be a daily process as you replay the offense over and over, God's Word will win eventually!)
Don't fake the "I am above reproach" approach. We are all human. We all fall short. Be honest with God and seek HIM to work on your heart. You aren't fooling Him anyway. INtegrity will last and Outegrity will be a passing fad.