Acronym for Ball Hard, Never Look Back.
The act of being in perpetual idgaf mode. Not the lazy, don't-want-to-get-out-of-bed-in-the-morning idgaf, but the high energy pimp kind of idgaf.
If you do end up looking back, you are no longer BHNLBing, and you immediately turn to salt.
Creezy Heezy: Yo, my boss just walked in on my fucking his secretary in his office
Otter: Whoa, so what did you do?
Creezy Heezy: I yelled at him: "wtf you doing? a little privacy please" BHNLB
Otter: so he fired you.
Creezy Heezy: ... yeah.