Onlookers passing by the Lampoon Castle Sunday afternoon were suspicious to see a trampoline gracing its front steps. They may not have realized, however, that the elaborate outdoor setup was part of yet another bad Lampoon joke.

This time, the prank lay in wait for roughly 200 fans attending a question-and-answer session with “Scrubs” star Zach Braff at the Brattle Theatre.

Shortly after 3 p.m., a member of the Lampoon told the fans assembled at the Brattle that Braff would not be coming to the venue as advertised, due to a “trampoline clause” in his contract that prevented him from answering questions without jumping up and down at the same time.

A Skype video call showing Braff on a trampoline outside the ’Poon Castle soon appeared on a Brattle screen.

The crowd sat mostly silent as Poonsters bandied questions about backflips and drug use, interrupting only to hurl sporadic boos at the screen.

The conceit from the Lampoon—a semi-secret Sorrento Square social organization that used to occasionally publish a so-called humor magazine—soon exhausted itself, and Braff made his way to the Brattle. His first act was to show the crowd a YouTube video entitled, “Girl Poots in Hot Tub.”

“If you remember nothing else from meeting me, remember this,” Braff said, soon before collapsing into peals of laughter at the video clip.

Braff then marveled at the success of the soundtrack for “Garden State,” the 2004 movie he wrote and directed. ”I won a fuckin’ Grammy for making a mix CD,” he said.

He also discussed his screenwriting process, a piecemeal approach of accumulating disjointed vignettes and compiling them into a single screenplay.

“I write things down on little strips of paper, in drawers in the house, and I just procrastinate until it’s just preposterous, and I have to write,” he said.

Braff also spoke fondly of his time on “Scrubs”—the NBC sitcom centered on hospital life entering its final season this fall—saying his job “paid way too much money to just act silly and stupid.”

Braff said a Broadway-style episode of the show called “My Musical” was his favorite since it let him “sing about poo,” and he talked of the show’s popularity among young audiences, saying that “if they had the little Nielsen boxes” in college dorms, “we might still be on.”

Audience members said they thought far more of the question-and-answer session than they did of the prank beforehand.

“I thought the Lampoon thing was hella lame,” said Teresa M. Cotsirilos ’10 after exiting the theater, “but I liked [the rest].”

The Brattle crowd then followed Braff back to the steps of the Lampoon, where Poonsters presented him with a baseball cap, a bowling trophy labeled “Al’s Birthday, 1994,” a mock degree in medicine, and an oversized model of an ice cream cone. Braff was then given the honorary title of “Ice Cream Man of the Day.”

—Staff writer Nicholas K. Tabor can be reached at ntabor@fas.harvard.edu.