Shout-Out: All the elements of the 'Just Another Girl' video are from one of the other music videos, except the big number 4 behind Dianna right as she starts walking over to 'Human', as far as I can recall. The most logical explanation, then, is that it refers to the actress' role in Film.I Am Number Four. The whole recreating music videos thing also links back to Glee. Just in case you thought she was Miley Cyrus for a minute there.
The lines "Jason's getting married in the blink of an eye/Got an invitation but I didn't reply/Tell your little brother that we put down the glove" could be a reference to Agron's little brother Jason. Maybe.