EASTER EGGS #20 and 21 - Multiplayer Mop Up
Here's one you can try from the menu screen. Choose "I17" ("i" as in the letter) for your multiplayer service tag. Oops! Seems that that particular code is already taken... by UNSC SPARTAN 117. You might know him as Master Chief... Oh well, better go for some immature "69" tags instead.
Finally, check out your Halo 3 Service Record on Bungie.net. Amidst all the Killing Sprees and Killtaculars (you get those, right?), you might notice a funny little cow named "Steaktacular!"
According toHalopedia, the medal is "earned by winning a multiplayer game by 20 or more kills. The description, 'Luke owes you a steak dinner', comes from a Bungie Humpday Challenge where a steak dinner was bet over a game, in which Will bet that he could beat another team, led by Mike, by at least 20 points. He lost 50-5." Ouch.