"Stay Together For The Kids" is also fairly sad, since it centers around a kid living with parents who argue a lot and are only together because they don't want their child to grow up in a broken home. It does NOT help the song was actually written by Tom De Longe about his experiences to it, seeing how his parents ended up divorced when he was a teenager.
"Man Overboard" is particularly sad. If that song really is about Scott Raynor, the original drummer (which he seems to know it is), it marks the day when Blink officially forgot about Scott.
"What Went Wrong" is also particularly sad, as it seemed to have been made for the Blink break-up — and was completely depressing for that reason. Then the reunion came, and... yeah.
"Not Now", as well.
"What's My Age Again" is surprisingly melancholic - it's telling the story of someone whose immaturity is no longer funny or interesting, just irritating, and ends up underlining how pathetic holding onto youth looks like past a certain point. The opening arpeggios don't help either.