When someone thinks about the past way too much, to the point where it gets very unhealthy for them.
90s kid: I really miss the 90s. Things back then were SO much better.
2010s kid: Dude, EVERY decade has bad things happen in them. Get over it already. You only live once so don't waste it on living in the past so much. I swear you 90s kids are so overnostalgic.