"888888888" is used on nicovideo.jp at the end of videos (usually songs) to represent clapping, due to the fact that 8 in Japan is pronounced "hachi", which sounds similar to "pachi", which when translated, means "to applaud or clap".
bozo from america: WHY IS EVEFRYONE SPAMMING 8????//?///
end of video: 888888888888888888888888888888888888888888888888888888
888888888888888888888888888888888888888888888888888888888888888888888888
end of video: 888888888888888888888888888888888888888888888888888888
888888888888888888888888888888888888888888888888888888888888888888888888
by CellieConal November 1, 2020
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