After a long night of drinking one will black out from drinking large amounts of alcohol. If one wakes up the next morning remembering nothing, but with a shit in ones pants then one has "browned out."
"Dude I totally am going to brown out tonight. I just ate a ton of taco bell and plan on drinking a ton!"
Less intense than the experience of "blacking out" when drunk and not remembering portions (or all) of your night, "browning out" occurs when you don't remember something until someone brings it up. It's not a complete blackout, but partial, because you remember once someone refreshes you.
I didn't even remember making out with Bryanne until J-Lo told me (it must not have been that good)! I definitely had a brown out last night.