Green’s Dictionary of Slang

B.C. adj.

1. extremely old [chronological notation BC, before Christ].

[UK]Sporting Times 5 Apr. 1/3: Rub up your B.C. Fashion Plates: your ‘Myra’s’ off her Cabase!

2. old-fashioned [i.e. before computers].

[SA]Sun. Indep. (S.Afr.) Life section 27 Jan. 2: He wants to prove he can fix it faster than your eyes can follow him [...] to make more money out of another befuddled BC (before computers) twit.