User blog comment:Fintin/Revisiting Barty's DF fruit/@comment-5386071-20130508164315/@comment-7614831-20130508175433

Every character who has used Busoshoku Haki to defend themselves against an attack so far have at least used their hands to block the attack, a classic example being when the three Admirals blocked Whitebeard's attack (in episode 473 and chapter 564, if you're into references in a big way). Even Sentomaru's ultimate guard seems to involve both hands (skip to 5:45 in this video: https://www.youtube.com/watch?v=t8R_To9tz0I ). Bartolomeo, on the other hand, had his back turned and was taking a leak when Hack attacked him. This is not to refute that he has trained himself to use Haki in a different way, but it's unlikely.