The 100 emoji means 'keep it 100' — keep it real, keep it authentic, 100% true. Sending the 100 emoji is an emphatic agreement, like nodding very hard. 'You're right ?' means 'you are completely right'. It originated in African-American Vernacular English and went mainstream through hip-hop and basketball culture in the 2010s. No hidden meaning. If your teen uses it under a friend's strong opinion, they are agreeing forcefully. Often shown with two red lines underneath, which simply emphasise the perfect score.