The same notes in the melody. I'm surprised you can't hear it at all haha (It's when I think he says "Fabulous Night" and when Katy says "Last Friday Night")
I agree with you, with that EDM sound and those chords, it definitely sounds just like a western pop song (probably why I dislike it so much, lol). And it does sound a little similar to Last Friday Night, at least to me as well.
Fabulous Night? What I keep hearing is "Fuck last night"