Dank memes. But why?

On the internet, when talking about memes, a "dank meme" means old and out-played. According to Wiktionary, "dank" means "to moisten, dampen; used of mist, dew etc.". This doesn't sound like the definition of "dank" on the context of memes at all.

I would like to know why the word "dank" was chosen.

Solution 1:

I would go out on a limb and say that the metaphor underlying dank here is of something old and relegated to a damp basement, edit: or something wet and smelly like vegetable matter in a wet place.

Dank weed is a 150-year-old collocation referring to such plant matter, and that's how it got applied to (top quality) marijuana, whose skunky smell and funky appearance resembled a weed from a moist place and beginning to decompose.

“Dank Memes” is an ironic expression used to mock online viral media and in-jokes that have exhausted their comedic value to the point of being trite or cliché. In this context, the word “dank,” originally coined as a term for high quality marijuana, is satirically used as a synonym for “cool.” http://knowyourmeme.com/memes/dank-memes

So, according to knowyourmeme.com, "dank" is a term of approbation (like "cool") but is being applied ironically to mean just the opposite, not cool.

Solution 2:

I always thought it was borrowed from a cannabis reference 'dank weed' being cannabis that has strong and appeal fragrance.

A quick google of 'dank weed' suggests that dank is indeed being used in this context.