The word has been derived from the word msunu which is a slightly offensive word to refer to the anus.
The word is usually used in reference to anything that you strongly disprove of.
Twitter will now let you add photos, videos, or GIFs to Retweets. But no Edit button, what kind of msunery is this?😂
— [L]e[S]e[D]i (@_Hybreed_) May 6, 2019