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A person who has become obsessed with the famous What's 9+10? 21 vine, they will often repeat the lines in the vine over and over again while still thinking its super hilarious. They also like to use 21 in almost every math situation ever. 9+10ers are considered to be extremely annoying by other people.
9+10er: Hey dude?
Person: What?
9+10er: What's 9+10 (silent laughter)
Person: (sigh) Get a life you 9+10er
by NoNeedFriends July 20, 2016
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