Favourite visual gag?

every time someone killed themselves listening to Ted Striker's life story.

the granma skeleton was 10/10

Gotta be the smile and cigarette on the automatic blow up pilot.

Robert Stack removing his sunglasses while emphasizing a point, only to reveal another pair of sunglasses.

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The random topless woman.

SOOOOOOOOOOOOOOOOOOOOOOOOOO many.

Um.... the Autopilot.

The Ethel Merman cameo:
https://www.youtube.com/watch?v=ZmZdqsCW8vM

Even if you don't know who Ethel Merman is beforehand, this is still legitimately one of the single, gut-busting, funniest things ever put on film. Instead of Lt. Hurwitz merely singing "Everything's Coming Up Roses", we have the actual Ethel Merman playing a shell-shocked male war veteran. Just the sheer randomness and absurdity of it all as well as Ethel's loud, brassy singing makes her come off like a ham. Isolated, it just looks like Ethel is some crazy woman performing to an invisible audience.

I'm quite partial to the 'JAWS' inspired opening scene.