A portmanteau of "Karma" and "Armageddon." References "shit hitting the fan" in an extreme way while acknowledging one's contributions to that event.
Specifically, when all the (usually unpleasant) stuff you've done comes back to you at once.
The only way out is to take your licking, batten the hatches, pull back, and deal with the stuff one by one.
Man, my license was revoked for not paying those speeding tickets, my car got the boot from those unpaid parking tickets, bill collectors are calling, work's a mess from my calling in "sick," and my girlfriend found out about the affair when the other girl stopped by our place... Argh, it's karmageddon!
Lord Karnage is an omnipotent ayatollah of Get-The-F&#k-Outta-My-Way whose awesomeness rivals Chuck Norris but his popularity is much, much, much less.
Just the fact that you had to look up Lord Karnage warrants your doom. Because you're reading this, you will be force-fed to his army of robotic alligators named Charlie I-VII. After that, your remains, if any, would be electrocuted by his robotic eels and then vaporized.
The desired outcome of an act of kindness, or the undesired reapage of a nasty deed. A Pauly Shore way to saythe word "karma." It's also fun to say because people mistake it for the word "carnage."
Dude, if you would do me a kindness, you might just reap you some good karmage.