The Flash Supergirl Musical Crossover: 14 Easter Eggs & References In 'Duet' You Need To See
3. I'm Not Supposed To Do That Anymore
Sticking with the Super Friend song (in fairness, it's utterly brilliant, and probably the highlight of the episode) and there are a couple of brilliant in-jokes within the lyrics.
Kara sings "And if you're not there in time you can just go back in time, and give it another shot." To this, Barry hilariously replies: "I'm actually not supposed to do that anymore."
The line is a reference to just how many times Barry has used his time travelling powers, and just as often managed to completely f**k things up, with the catalyst for this season being Barry going back in time to save his mother and creating Flashpoint.
Just as good is a later line, after Kara sings "And if you ever need a helping hand..." to which Barry responds "I'll be there in a Flash." Barry making Flash/running puns is nothing new, given it's been a part of the character throughout the series, and indeed in the comics as well, and certainly the Young Justice animated TV series.