ガチムチ Gatimuti Gachimuchi ガチムチパンツレスリング レスリングシリーズ gachiGASM 哲♂学 哲学 御三ゲイ
Gachimuchi (or Wrestling Series) is a memetic universe which revolves around male porn actors (mostly from Can-Am Productions) flexing their muscles, wearing and doing BDSM stuff, and doing gay pants wrestling (from where the tag gets its name, "Gachimuchi" meaning buff man in underwear in Japan) in homoerotic films taken out of context.
The meme originated when Niconico members uploaded a video of Billy Herrington and Danny Lee doing pants wrestling under the title "本格的 ガチムチパンツレスリング" (Professional Pant Wrestler Fighting Seriously) in 2007. This later spawned tons of parodies around pants wrestling and related people that acted in non-pants wrestling porn with a pants wrestler as an actor in the aforementioned porno.
It is often paired with Manatsu no yo no Inmu (Inmu-chu) and Kuso Miso Technique (Yaranaika) as the "Holy Homo Trinity" (御三ゲイ), since all three were well-known homoerotic memes that were popular within Japanese communities in the 2000s.
While Gachi parodies did find their way outside of Japan, most prominently between 2007 and 2012, it wasn't until later from 2015 onwards that it spread even further under the name gachiGASM (named after the BTTV emotes for Twitch.tv featuring Billy Herrington's iconic face) and spawned countless more sub-memes.
While Gachimuchi's popularity has decreased with the Japanese (being supplanted by Inmu on Niconico), Gachimuchi is currently extremely popular internationally. On the Chinese video site Bilibili, the Chinese started making parodies of their popular TV series and movies, and also parodies of Japanese anime. Many Gachimuchi videos became some of the most viewed videos on Bilibili (one having had over 5 million views). This popularity would, however, lead to Bilibili attempting to squash the community on the site, leading to it dispersing across other Chinese communities. It also became popular in Russia, where a live-action parody and various music remix was made of it in spite of the country's anti-homosexual laws.
The tag used for Gachimuchi on Bilibili and in Chinese communities is 哲♂学 (Learning♂Philosophy).