"That proves it... This must be a hallucination." (Mind-wiped Artemis' reaction to the Bizarro Episode culminating in being saved by a talking rear end (Mulch Diggums hanging from a rope.))
The entire conversation between Gobdaw (possessing Myles' body) and Artemis in The Last Guardian. Artemis essentially trolls Gobdaw into revealing himself after pretending his spirit had left Myles' body.
This bit from early in The Last Guardian:
"Hey," snapped Holly. "This is not the time to blame Artemis."
"Thank you," said Artemis."Finally."
"There will be plenty of time to blame Artemis later, when this is resolved."
Especially funny because, for once, Artemis has done nothing wrong and is not even slightly at fault for the current situation.
"I am Butler. Everything I say sounds tough. Now, get out of the lake, fairy."
Myles and Beckett's reactions to Artemis putting a combination lock on his lab door - Myles works out the combination after three days of work and several rolls of toilet paper, and Beckett digs a bear trap for Myles and gives him the ladder in exchange for the code.