A Kohen and His Colorful Socks

There are many complex halachos about interrupting one’s prayers for various responses. At some points in davening, it is forbidden to respond, “Boruch Hu u’baruch Shmo.” At other points, one cannot even respond amein. At some points, virtually every response is forbidden.
Which point during davening would one assume would be most restrictive?
A) Birchos Kriyas Shema B) Silent Shemoneh Esrai C) Kriyas Shema D) A Yisrael listening to Birchas Kohanim.
The answer is surprisingly D, Yisrael listening to Birchas Kohanim. The Gemara discusses various verses that a Yisrael may recite while listening to Birchas Kohanim. (Sotah 39b-40a). Rebbe Chanina Bar Pappa, however, strenuously objects to their recital. “Could there even exist a servant whose king is blessing him, and he doesn’t listen?!” Hashem is blessing us, and we should be preoccupied with reciting pesukim?!
Rebbe Chanina Bar Pappa’s reasoning is codified by the Mishna Berura. (128:102) There are differing opinions about whether or not is appropriate to recite the pesukim while the Kohanim are singing. However, while the Kohanim are actually blessing K’lal Yisrael, those verses may not be recited.