Drinking and staring at the ceiling, knowing that true love doesn't exist in this world.
For real though, totally bummed. No matter how Charlie ends up at the end of the show (probably with Waitress who in some stupid turn of events realizes he's perfect for her etc etc) he will never be with the person who most understands and likes him for who he is. All those years huffing glue and throwing rocks at trains together, wasted. Also Dennis already has Mac under his thumb so that sucks for Mac, he's probably going to become a boring housewife.
Aww shit, I'm gonna go rewatch season seven...