Complex sentence: Lois sneaks into the concert intending to seduce Bieber but Peter bursts in and beats him up and demands that Lois come home and start acting her age, but she refuses, citing what he said to her.
Split into simpler sentences: Lois sneaks into the concert intending to seduce Bieber but Peter bursts in and beats him up. After Peter demands that Lois come home and start acting her age she refuses, citing what he said to her.