The feeling you get when you come across an old friend on Facebook and realize that their life turned out way better and is more interesting than yours.
Joe: "My wife left me for another woman and my kid should be out on parole next summer. That, and I almost got my mullet grown to the perfect length. So what have you been up to?"
Jim: "I ended up getting married to a supermodel and moving to Monaco after selling my shares in MSFT. Currently doing volunteer work to eradicate poverty. Oh, you may have also seen me in the news recently during my kid's Nobel prize nomination."