The full names of BK in Tianjin dialect are B (read aloud) and K (read softly). It should be in Tianjin dialect, which is more vivid and has similar meaning: a series of sons of bitches.
BK: synonymous with swearing, used in the second person and the third person. Example: Why did you (the second person) come here? /The world is going to be thrown away. I have already issued (sound) BK.
Extended data:
The characteristics of Tianjin dialect are mainly reflected in pronunciation.
(1) In Tianjin dialect, some initials are rolling Chinese characters, such as Zh, ch and sh, which are pronounced as "Z", "C" and "S", and the initials are flat, such as "Zhan", while "Zan" is pronounced as "Zhan" in Tianjin dialect;
(2) Putonghua has the initial r, Tianjin dialect reads zero, and vowels are used instead of consonants. For example, benevolence, heat, softness and moistening, while in, that is, you and Yun, is pronounced in Tianjin dialect.