Mark Wilson, of Coolyermer, Letterbreen, denied intimidating Lyndsey Clarke during a St. Patrick's Night out at a bar in Enniskillen.
However, he was found guilty of the offence, sentenced to four months in prison, suspended for two years, and fined £250.
Miss Clarke gave evidence that she had been assaulted by Wilson's brother, Jason, in August 2011, and the case had still to come to court.
She said that on St. Patrick's Day she went to the Bush Bar in Enniskillen and while on the dance floor close to the smoking area met Wilson.
She said she "freaked out" and was scared when he told her: "You're nothing but a w--ker. You better drop the charges or you'll be left a lot worse."
She told the court she assumed it was a threat to withdraw her complaint against his brother.
The court heard that there was a history to the assault case with the PPS (Public Prosecution Service) writing to Jason Wilson last December, informing him that he was not to be prosecuted. However, when Miss Clarke complained about the decision the PPS wrote a second letter to Jason Wilson in April of this year, telling him he was to be prosecuted for the alleged assault on her.
The prosecutor put it to Miss Clarke that it was "absolutely ridiculous" for Mark Wilson to confront her in March and suggest she drop the charge because at that time, as far as he and his brother were concerned, there was to be no prosecution.
"Well that's what he said to me on that night," replied Miss Clarke.
The court heard that she had initially named Mark Wilson as her alleged attacker and when asked by District Judge Alan White how she made the mistake she replied: "I had head injuries."
Defence barrister Stephen Mooney put it to Miss Clarke that when she was informed the charge against Jason Wilson had been dropped she initially asked the PPS, through her solicitor, to review the decision. When that didn't bear fruit she got a local politician to intercede on her behalf and had "pushed the case as far as humanly possible" to have it reinstated.
Miss Clarke told the court that between August of last year and St. Patrick's Day this year Wilson had passed her in his car on a number of occasions, giving her "the fingers" and shouting: "Tramp." When she went into Asda, where he and his brother work, he would laugh at her.
Mr. Mooney suggested she could go to Tesco instead and that she was going into Asda to "up the ante".
"No, definitely not," replied Miss Clarke.
She was asked why it had taken her a four weeks to go to the police and complain about the incident in the Bush Bar.
"Because I was scared," she replied.
Her friend, Sabrina Neill, said she was with her in the Bush Bar and heard Wilson make the remark about dropping the charges.
She said he also told her to get Miss Clarke to drop the charges and she "felt scared" for her friend.
She told the court Miss Clarke had burst into tears and she had comforted her. She denied calling Wilson a "rat".
She said that in the four weeks between the incident in the Bush Bar and it being reported to the police she and Miss Clarke had discussed what had happened and it was she who persuaded her to go to the police.
Wilson told the court he was very close to his brother and that in December of last year was aware that the charge against him had been dropped and in April of this year became aware the case had been re-opened.
He accepted that he was in the Bush Bar on the night in question but said nothing of any significance happened. He said he didn't see Miss Clarke and her friend and didn't make the remark about dropping the charges.
The District Judge referred to the delay in Miss Clarke going to the police and her failure to report other alleged incidents "but I didn't get any impression she had come here to commit perjury".
He said he found Miss Neill to be a "truthful" and "compelling witness".
Turning to the evidence of Wilson, the District Judge said: "I don't believe him."
He said he was satisfied Wilson had approached Miss Clarke to persuade her to drop the charges against his brother.
The District Judge said that whether Wilson believed the charges had been dropped or not or alcohol was a factor he was satisfied the teenager committed the offence.
"I regard any attempt to intimidate a witness as extremely serious and a matter the court will not tolerate," he stated.
He sentenced Wilson to four months imprisonment, suspended the sentence for two years, and fined him £250.