An emoticon tupo is a tupo made when someone fails to type a character that is required for a certain emoticon, or makes an emoticon they weren't intending to.
Person 1: "I can't remember my score on 309, but I don't think it's over 1M O_ "
Person 1: " * O_O "
Person 1: "I failed Level 336! XD "
Person 1: " * DX "