The phrase "thorny topic" refers to a subject or issue that is difficult and controversial, and often causes problems or disagreements when discussed. Full definition
So much so, in fact, that I'm doing another one with Norm on 24 May, this time on the equally thorny topic of legal directories. (motivelegal.com)
At the same time, raising the age of criminal responsibility was especially thorny topic for Cuomo and Democratic lawmakers, making a compromise on the complex criminal justice issue difficult. (nystateofpolitics.com)
As Mr. de Blasio prepared to take off - topic questions — on stop and frisk, raises for elected officials and other thorny topics — Ms. Quinn simply bowed out. (observer.com)