The meme spammer can often be found lurking in forums, waiting for the perfect moment to spring up, and shoot their meme gun. If they are successful, someone will succumb to the meme and begin to use it. This is how memes are spread.
But meme spammers are not your run-of-the-mill forumite. Your average forumite will occasionally use a meme to add to the conversation, or to make a witty point. Consider them snipers, or at least, looking down the sights of their meme gun.
Meme spammers are the same sort of people who spray-and-pray in MW2. Except their meme gun will never run out of bullets. And they shoot from the hip. With akimbo meme guns.
Rather than even attempt to reproduce the horror that is a meme spammer, this XKCD comic about gets it right.
So, now that you know how to identify them, how can you counter them?
That's the only reason you're reading this, right?
Well, it's really not too hard. Just like a MW2 sprayer, you can just knife them. With words!
Okay, I've carried this MW2 metaphor for too long. Stopping now. Time to shoot it down like a chopper gunner.
Anyways, once you have identified the meme spammer, as with any case of AIDS, you have several courses of action.
The Troublemaker - Reply to the post before theirs, and as a post-script, add a link to a random youtube video, telling them that their memes are outdated, and that this is the newest one.
The Troll - As above, but instead of a random video, link them to something which will cause them to need mind bleach, and lots of it.
The Apathetic - Ignore their post, and get on with your life. Someone else will handle it eventually. Or not. It doesn't matter, you know.
The Bragger - Out-meme them. How many meme's are necessary? Over 9000.