Me personally I couldn’t transfer my profile to my new xbox. I made a new silver account but no war games for a while:(.
So If you had a fail on your launch day lets here it!
First time I picked up the sticky detonator.
Shot on the floor in front of me, wondered what the -Yoink- it did. Tried shooting another time. Suicide.
My wifi network has been glitchy, so at first my wireless adapter wasn’t working and I couldn’t sign onto XBL. I finally got it fixed long enough to go through two levels of the campaign, but then when I tried to do War Games, I was kicked off.
I have since decided just to play with an ethernet cable hooked directly into my 360.
At the last 5 seconds of the second mission and the game crashed my xbox. I couldn’t even dashboard quit.
Then when I restart everything and complete the entire game on Heroic it still doesn’t have my mission 2 as completed. Weird launch day fail.
my stats are not updating … and I really want to see after 6 games how I’ve done =(
My xbox was a 20 gig one. and it litereally died playng halo 4 at midnight (australia) so i had to spend $340 (australian) on a new xbox.
EDIT: It died by only being able to play small myultiplayer maps and freezing in the first 5 mins of campaign. I deleted all halo data and resaved disc 2 but it didnt help, additionaly i deleted all my downloaded preorder/LE codes so i lost them. However I found out i could redownload after transferring my account to my new xbox
I picked up an Incineration cannon and thought, “This looks interesting” and shot point blank at an enemy. Killing myself.
Playing CTF on Ragnarok, flying the Banshee over the enemy base and decided to drop into the flag-zone from above, landed in a mancannon as did my vehicle shortly thereafter which was propelled rapidly into my reddening face resulting in a “Suicide!”.
Killed myself with the sticky detonator and incineration cannon. 
I feel like everybody killed themselves with the incineration cannon atleast once!
I jumped off the edge trying to avoid becoming infected in a game of flood.
My launch day fail would be not getting the game delivered
I had a few suicides, but the worst fail of the launch day is the servers. Oh well, got some time to play campaign. Two more missions to go heroic co-op.
My launch day fail was in my first game of Big Team Infinity Slayer. I went to run over a member of Blue Team with my Ghost and ended up running down two members of my own team instead. 
First match i ran out the spawn thinking “ive been playing since halo 3 ill own them all!” run round the corner and greeted by a energy sword to the face.
Accidentally used thruster pack in mid-air throwing myself backwards off the map (Adrift) lol.
First match on Complex, I grab a Ghost and see a ramp. Naturally I yelled “Yeehaw” and went for it. Hit a wall, fell off the map. My friend watched the whole thing and is still laughing.
You know when you first see the covenant boarding the FUD? Well I was looking out the window, right? I told my friend “C’mon I don’t want to die in here.” Lo and behold a split-second later, I started walking, and I get killed by a frickin’ flying box.
went to EB games at 8am, it opened at 9am 
Most of my friends were playing the campaign and only 1 wanted to play wargames. Stuck with bad randoms… -_-