So there's this thing going around about how apparently people my age see the thumbs up emoji as passive aggresive, it that's true it's stupid. What I hate is when people just reply "yes" in a casual conversation. ESPECIALLY if it's all lowercase. If you don't really have anyhting else to say, just say yea, it's more informal, if not just a reaction/like. I get that the latter might not always be an option, but just saying 'yes' comes across as so like, stiff to me.