to get so chemically altered that you don't remember anything.

Blacking out is what happens when you drink too much and you are somewhere between shitfaced and dead, and the next morning your friends kindly let you know that that tree you thought you were pissing on was actually a parking meter.

It has nothing to do with butthurt bitches turning off cell phones, computers, or whatever to ignore their (ex-)boyfriends.

When you get so wasted/faded that your brain stops storing conscious memory's, and anything that you do while blacked out will not be remembered tomorrow.
"blacking out is the action that leads to being blacked out."
Black outs can be very unsettling/dangerous, but also create potentially hilarious situations.

when one consumes so much of a substance (typically alcohol) that one cannot remember one's actions at a later time, be it later in the night or the morning after

see also time travel

To drink so much alcohol that you dont remember a thing.

To turn off any device that people can reach you with (cell phone, two-way, computer, home phone, morse code, etc.) in order to avoid someone.

When a female leaves a scoial establishment of any kind with at least one black man--and you just know she'll be hurting tomorrow.