BDSM - bondage discipline sadism masochism; B&D with the specific inclusion of the infliction of punishment by a sadist on a masochist. Usage example: "This is a bdsm room and may contain pictures or activities of a sexual nature. If you have chosen this room in error please click here".
BF - boyfriend.
blue screen of death - when this happens to your computer, close one or more programmes. It's not actually fatal, despite its name.
board - messageboard; an address in cyber-space where comments and replies to comments can be posted. Many boards are publicly accessible but some have passwords to restrict them to members-only use. On all boards, brevity is the soul of netiquette. Long, rambling and pointless posts are looked upon with disfavour and rarely attract replies.
bottom - See sub.
boyf - see bf.
BRB - be right back. The person is on a toilet break, pretending they are working because their boss is in the room, taking their dinner out of the oven before it burns, retrieving a file or pic for you to look at, emailing you, ghosting in another room, etc.. They will probably be back within 3 minutes. When is it considered impolite to "brb"? When at a crucial point in cybering.
browser - the software thingy that lets you get onto the internet and look at websites like this one.
B4 - before.
BEG - big evil grin.
BFN - bye for now.
BIBO - beer in beer out.
BMOC - big man on campus.
BS - bullshit.
BTDT - been there, done that.
BTSOOM - beats the shit out of me.
BTW - by the way.