8 - comes from "ya" in the japanese number "8", when read as 'yattsu'.
0 - comes from the roman letter "O."
1 - comes from the "I" in the japanese number for "1", 'ichi'.
The word can be thought of as shorthand, or a code word for yaoi.
Hey LuvEX, did you read the last yaoi comic in BL Gold?
LuvEX: Hey, use 801 instead plz, my mom's in the room.