[ATOP] "At time of posting..."

[ATTN] "Attention"

[Aunt Tom] {n.}, {slang}, {originally from Black English} A successful professional […]

[AUP] "Acceptable Use Policy"

[AYBABTU] "All your base are belong to us"

[Azn] adjective short of "Asian"

[B&] "Banned"

[B/T, BT] "Between" or the BitTorrent peer-to-peer file-sharing protocol.

[B00t] Opposite of "w00t". Can also describe kicking people from game […]

[B0rk, b0rked, to b0rk] broken, to break. A b0rked system refuses […]