None of those mashups convinced me of anything. Although I do think some of Taylor's songs sound like they could be sung by Avril, moreas a general sound rather than specific songs
The song received mixed reviews from music critics, some citing its similarities to Toni Basil's song "Mickey", and comparing it to her previous single "Girlfriend". Commercially, the song failed to make any significant impact on the charts, peaking outside the top-forty in most countries.
LAWL. It's a sampled beat you idiot. Butch clarified that he was licensed to sample the Hey Mickey drumbeat. There is no rip off involved
Shake It Off was influenced by Hey Mickey, if Avril sampled it then that explains the "similarities" between the songs. Though I still don't hear it in the chorus/vocals/anything else but the beat.
It's in Butch Walker's book that he licensed the beats. Not trying hard, just taking a direct quote from Butch himself 