This takes place right after Eden Prime. The first trip to the Citadel.

Anderson hit the button for the elevator.
"Knock knock," Trick said.
"Who's there?" Anderson questioned like knock-knock jokes were normal procedure while waiting for an elevator.
"Little Old Lady," Trick replied.
"Little Old Lady Who?" Anderson asked.
"I didn't know you could yodel, sir," Trick said with a grin.
"That's an old joke, son," Anderson said with a small smile.
Ashley shot Kaidan a curious look. Kaidan just shrugged.

After the meeting with Udina, Anderson dismissed Trick, Kaidan and Ashley and told them to meet him at the tower. After Anderson and Udina left, Trick walked over to a terminal in the office.
"Have you served under Anderson before?" Ashley asked him.
"No," Trick replied focusing on the terminal. "He's an old family friend, though."
"That would explain the knock-knock joke, then," Ashley said.
"Huh?" Trick asked giving her a curious look.
"The knock-knock joke you two did while we waited on the elevator," Ashley said. "It makes sense because you two know each other. Like you've done it before."
"I guess it would make sense," Trick said walking away from the terminal. "But I just did it randomly. Kind of surprised Anderson went along with it. I just like knock-knock jokes."

Kaidan and Ashley watched Shepard leave the office. He was whistling a tune Kaidan vaguely recognized.
"There might be something wrong with him," Ashley whispered.
Kaidan opened his mouth to reply but stopped when Shepard stuck his head back in the doorway.
"Come on you two," he said. "We have a very important meeting to get to."