Some DMs like to make rolls to determine if something ridiculous happens when a player does something the DM doesn't like, such as making a bad pun.
He or she rolls a d20. If the result is below 6, a minor meme happens. These are small things that don't typically have an influence on gameplay, such as a small rock falling on the target player out of nowhere and deals 0 damage. If the result is 1, a major meme happens. This could be anything from a merperson falling out of the sky for no apparent reason and hitting the target player. To having all of bones in the target player's body spontaneously disappear.
Players must be weary of what they say and do when dealing with a DM that employs Memes.