Contrary to what you may think, the Bible has never shied away from talking about sex. In fact, the entire Song of Solomon is dedicated to describing a couple getting it on, complete with lines like "I am a wall, and my breasts are like towers". This verse is particularly explicit, though, informing us that Egyptians are hung like farmyard animals, and can ejaculate in quantities to rival the annual flooding of the Nile.
Keep in mind, the Egyptians were the Jews' former slave masters and are the bad guys in this story. So, you know their reputation for supreme endowment was well earned when the worst their enemies could say was, "Go on! Go back to those big-cocked bastards! I hope you're happy with their enormous dongs."
The old Egyptians didn't exactly run from their reputation. Egyptian ruins are littered with statues like the one on the right (this one is Min, the god of huge dong-having). They even invented the phallic obelisk to advertise it (picture the Washington Monument, that's an obelisk). That was their statement to the world: "Gaze upon our dick tower and despair."
This passage creates a problem for many new Bible readers. Once you've read this, it is impossible to go back and read the above story of Moses killing the Egyptian guy the same way. When it speaks of the Egyptian beating the Hebrew slave, you have no choice but to imagine him turkey slapping the man. If anything, however, it makes Moses' deadly intervention all the more justified.