Ideally, there should be a BYO for every occasion, even your own death. Here are two Japanese BYOs to serve two of your many moods:
For a date: K
This upscale Soho sleeve is intimate but not cloyingly romantic -- and it's mostly two-tops, so there'll be no groups of drunks to make you wish you were out with a group of drunks. Grub highlights include "Lobster on a Spoon" w/ chopped jalapeno and mango dressing, a pepper-encrusted Kobe steak, and a "Sushi Love Boat" -- an exciting and new platter that'll satisfy any woman's taste, unless she hates boats, or love.
For a group: Kamui Den
This unmarked hole-in-the-wall has a wooden banquet table big enough for you, 12 friends, and ten gallons of various and sundry booze. But despite the austere setting, the food's great, with a full sushi roster and apps like shrimp balls (careful, as these come out hot as balls). There's also shabu shabu -- a medieval-style dish in which diners dip their own meat/fingers in boiling broth.
Finally, remember: opting for K shouldn't prevent you from Japanese BYOing's lifeblood, sake bombing -- if your date doesn't like it, you can set a course for adventure, straight to your idiot entourage at Kamui.