"Oh and the redhead said you shred the cello and I'm jello baby" means exactly what it says. A redheaded girl (who I'm going to guess is the girl who River's wrote the song about's friend) told Rivers that she (the girl who the song is about) could play [shred] the cello really well. Rivers really admires that and finds it attractive and as a result he's "jello."
"Oh and the redhead said you shred the cello and I'm jello baby" means exactly what it says. A redheaded girl (who I'm going to guess is the girl who River's wrote the song about's friend) told Rivers that she (the girl who the song is about) could play [shred] the cello really well. Rivers really admires that and finds it attractive and as a result he's "jello."