* 69: The sex number.
* 420: The weed number.
* 300: A reference to the movie 300, often associated with a dramatic, shouting tone ("This is Sparta!").
* 80085: When typed into a calculator and turned upside down, it spells out "BOOBS."
* 42069: A combination of the weed and sex numbers, a culmination of the two primary jokes.
The meme is less about the single, long string of digits and more about the collection of these well-known internet jokes and their placement in a sequence. It's a kind of "super-meme" that combines several popular memes into one.