Derogatory. Foolishly obedient. Like a dog wagging its tail.
Based on the song titled 'Waggy' from
Blink 182 on the album Dude
Ranch. Despite the official reason for the title ("I made this word up while belching, and wanted to title a song with it. This was the song that got stuck with that title." - Mark Hoppus), the Lyrics of the song suggest that the guy was taken for a fool several times after being foolishly obedient/
loyal, with 'Waggy' being a suitable derogatory name.
Julie: Hey Steph, you think you are going to have enough money for our big party night?
Steph: Yeah always, I will just ask
Mark to give me some, he can give us a lift there, then pick us up later.
Julie: He must be Waggy as fuck.