When Poseidon tells Percy to clean his cabin.
Percy be like:
" No, I will not clean the cabin. Deal with it."
"I am also proposing to Annabeth whether you and Athena like it or not. Deal with it."
"I am the most popular guy at camp and everybody wants to be my friend. Deal with it."
"I defeated Kronos, and helped defeat Gaea. Deal with it."
" And I will not clean my cabin. Deal with it!"
"I AM THE KING OF SASS. DEAL WITH IT!!!!!!!"
The Poseidon is all like:
" I am your father. Deal with it, and clean your cabin."
Percy spends the rest of the afternoon with a magic broom and mop (courtesy of Poseidon) which doesn't let him stop cleaning until the cabin is sparkling.
