The recitation of Birkat Ha’mazon, in many situations, is required Mi’de’orayta – by force of Torah law. As such, it should be treated with particular seriousness and reverence, which includes ensuring proper attire. Just as one must be dressed properly when he prays, he must also be dressed properly for the recitation of Birkat Ha’mazon. In fact, as prayer might be required only Mi’de’rabbanan (by force of Rabbinic enactment) whereas Birkat Ha’mazon constitutes a Torah obligation, there is room to argue that proper attire assumes even greater importance when reciting Birkat Ha’mazon than when praying.
Accordingly, Hacham Bension Abba Shaul (Israel, 1923-1998), in his work Or Le’sion (vol. 2), writes that one should not recite Birkat Ha’mazon while wearing pajamas. This was also the ruling of Rav Shlomo Zalman Auerbach (Israel, 1910-1995), who added that one should not recite Birkat Ha’mazon in a bathrobe, unless one is ill and bedridden, in which case he should wear a robe over his pajamas when reciting Birkat Ha’mazon.
By the same token, Hacham Bension Abba Shaul rules that one who eats a sandwich at the beach must get dressed in his regular attire for the recitation of Birkat Ha’mazon. Just as one would not pray the Amida in a bathing suit or shorts, one should not recite Birkat Ha’mazon dressed in that manner, and therefore one who plans on eating at the beach must ensure to bring along a shirt and long pants for Birkat Ha’mazon. Of course, if one did not bring a shirt and pants, he should recite Birkat Ha’mazon in his bathing suit, as this is certainly preferable to not reciting Birkat Ha’mazon at all. But this demonstrates the serious approach taken by the Poskim regarding the respect required for Birkat Ha’mazon. Likewise, Hacham Ovadia Yosef wrote that it is proper to wear either a hat or a Kippa that covers the majority of one’s head for Birkat Ha’mazon.
Summary: One must be properly dressed for the recitation of Birkat Ha’mazon, and thus one should not recite Birkat Ha’mazon while wearing pajamas, shorts, a bathrobe or bathing suit.
