I anticipated the punchline in advance, and still found it funny. It probably would have been funnier if I hadn't seen it coming.

I immediately proceeded to discuss it with a friend, who couldn't understand what was funny about it at all.

I came up with another joke to explain to her what's funny to me about this one. I find them I find them funny for similar reasons.

A man walks into a control room. There is a big red button labeled "Nuclear Launch Button." He walks up and presses it.

A display screen next to the button reads "Input password." There is a number panel below the screen. He searches around the room, and finds a locked desk. He jimmies it open, and rummages around through it. Inside there is sheet of paper which says "Nuclear launch password: 7831662"

He returns to the number panel, and punches in 7831662. The display screen says "Code confirmed. Press again to launch." He presses the button again. "Launching nuclear arsenal."

He stares at the screen in shock. "Aw shit.... I fucked up."