Reese Witherspoon's singing.
Did anyone else think she was the weakest singer of the cast? I didn't feel like she had any pitch, which is why she sounded so obviously auto-tuned, which didn't help matters but that she also didn't know how to phrase her melodies. Her cover of Shake It Off really showed off her limitations as a singer. Maybe she would sound better with another song but even I don't know about that. After all, not every actor should be a singer (Johnny Depp is the golden boy for this) and Witherspoon was clearly out of her element here for me. I feel like even the filmmakers knew that, which is why they gave her character a singing partner in Nick Kroll to make it less noticeable.
Want three steaks?... My mistake. Four steaks.