Sam, lock horns.....means to become involved in a fight, argument, or competition with someone or something. Fighting animals sometimes get their horns stuck together (locked). That is where the expression comes from. The expression is fairly common in sports writing, and in business and political reporting. NBA Playoffs: Chicago Bulls lock horns with Miami Heat. Apple doesn't seem to be afraid to lock horns with any major company, and has recently gone head to head in a legal battle against Google. The two multinationals have locked horns over drilling rights west of the Shetlands. In football as in life, history has a habit of repeating itself. Portugal and Russia, who locked horns during the qualifying phase for the 2006 FIFA World Cup Germany™, again find themselves in the same pool for Brazil 2014.

no it is not a common expression lock horns it can refer to a fight or a dispuit, in an example they locked horn in a fight, Mary was so mad she locked horns with her boyfriend and would not back down.