For me, it's the dishonesty of facebook and instagram. The whole culture seems to be based around lying about misrepresenting how good your life is.

I love seeing a post about something that made a friend happy, but so much of the content on facebook is so obviously not an honest post about something that made somebody happy, but rather something they felt should have made them happy, or something that somebody else would be jealous of, or worst of all a brand trying to co-opt the "something that made me happy" style of posting, that it's ruined the few honest moments of joy.