KAREN: ...banana.
ME: Banana would be Byakuya's safeword.
SQUEAKER: ...ow.

(This will only make sense to us, but it will make me laugh hysterically for EVER.)

[EDIT] Uhhh, possibly additional context is required. Like, um, when you're fighting with Byakuya in the Bleach Wii games, he says, "Ow," in this slightly surprised way that is absolutely HYSTERICAL given the violence in that game.

And a further explanatory note on Banana is:
- somehow it became the official safeword of meat bamboo (I DON'T KNOW, I WASN'T HERE)
- during one of the Shinigami Zukan, Byakuya ends up at one of the Shinigami Women's Association Meetings (I DON'T KNOW) and basically sums up the history of people thinking he is massively ridiculous by saying, "Bananas are delicious and full of vitamins."