The F word is NOT sexual harassment, (unless directed at you in context) and to attempt to press sexual harassment charges against someone over that would be an even worse witness for our faith than using the word, ourselves, would be, at least in my opinion.
Now, if you are dealing with Catholics or Protestants who claim to desire obedience to God, you can hit them with Colossians 3:8. Don’t do that, however, when dealing with “casual” Christians, nonbelievers, or even while in the presence of “casual” Christians or nonbelievers, as such would be a poor witness to the faith.
If addressing someone, do it in private, as not to embarass or make an incident where the person needs to save face in front of a crowd. Ask kindly, humbly, and respectfully for that person please to not use that language in your presence. Most people will comply if you ask that way, even though they may accidentally slip up, if it is a regular habit for them to use profanity.
I tend to pray to God to forgive them, when I hear people use inappropriate language. It’s not my place, however, to try to police people’s mouths. I need to set the example, myself. I’ve actually had people apologize to me for using profanity in my presence, without me saying a word in complaint to them. I feel that we need to look at it as a challenge to present ourselves in such an innocent, pure, wholesome, yet NOT JUDGEMENTAL manner, that people will want to act in the most Godly way possible around us. The best witness to Christ that we can give in our lives usually doesn’t require words, in my opinion.