@Frank Apisa,
In general the practice of using "bad" as a synonym of (or, replacement of) it's (former) antonym "good" was revived in the 60's. I say "revived" because that substitution had occurred back in the 1920's, and probably even earlier.
It is not uncommon for those who feel oppressed to turn "negative" words into positive ones.
That's why homosexuals will frequently refer to themselves and others as "fags." Just don't let anyone else do it.
Same with blacks, and the word "nigga."
Not that "my bad" is supposed to mean "my good," cause it aint.