1. the song is a meme
- joke cuts of anime op's
- intentionally bad covers
- background song of a current meme
- etc.
2. I don't think there are many mapping styles that could be considered a meme apart from parody maps about other mappers or themselves.
3. The map is a meta joke about the community - like this honesty mapset:
beatmapsets/814850#osu/1909862basically if you intended the map as a meme. I guess there's also the ranked maps that become a meme, but in modding queues your map wont have that reputation yet.