Ooh lah lah!
Maybe Chopin's Fourth Ballade, Op. 52. That is a VERY opinionated piece. Some arrogant people think that it should be played metronomically, and think that their way iks the only way (the piano teacher I quit from, for example).
So yeah, if that's the case, then the "difficulty" the neighbor would criticize the student about would be like "Oh, you stupid little girl, you're speeding up.. and then you're slowing down.... then you're speeding up, then you're slowing down again... Chopin did not write that. See all the lines he put in? You have to follow them. NO SPEEDING UP OR SLOWING DOWN. ABSOLUTELY NO RUBATO" Or something like that.
That's my suggestion. But it would only work if the neighbor is an arrogant freak with no sense of music. She has to have A LOT of background in music, though, but she must be lacking in "musicality". Get what I'm saying? So if the neighbor doesn't meet that criteria, don't use this piece.