"Rebuke your neighbor frankly so you will not share in their guilt." (NIV)
Which to me places a requirement to be frank to my neighbours - i.e. everyone around me. As Christians, we know that God does not hate sinners - indeed He doesn't - He only hates their sin. Which is why He expects us to "Preach the word of God. Be prepared, whether the time is favorable or not. Patiently correct, rebuke, and encourage your people with good teaching." (2 Tim 4:2 - NLT) Sometimes we even need to correct, rebuke and even encourage Christians - to do what they should.
The bottom line is we must be frank -
honest, open and truthful - with others -
there is no excuse not to be.