That's one small step for (a) man, one giant leap for mankind.
Did Neil Armstrong say the "a" or didn't he? Judge for yourself when you listen to the original recording broadcast across the world on July 20, 1969.
Pete Conrad, the third astronaut to step onto the surface of the Moon, pokes a little fun at Neil Armstrong when he says, "Whoopie! Man, that may have been a small one for Neil, but that's a long one for me."
The calm and matter-of-fact conversation between the Apollo 13 crew and mission control (see the transcript here) when their No. 2 oxygen tank exploded belies the seriousness of the situation. Listen for the correct quote: "Houston, we've had a problem."