It is a naughty slang between native Chinese teens. It literally translates to "muah(kiss)". It can be found in the conversations between good friends( even same gender) and couples.
1.
-good night! 么么哒
-yup, you too.

2.
-Please bring me my computer,么么哒.

-okie
by Liu Yuhang April 24, 2017
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