My first kill was a betrayal by accident, lol. I was so determined to get a kill before dying first that I forgot to check what team I was on. My first enemy kill was full of blood pumping excitement as I out DMR’d someone at mid range. 
Descibe your first kill.
I may be wrong, but I thought there is no teamkill in Halo 4 ._.
Complex, central base were everyone hogs the roof.
I ran up the ramp to go inside, other guy ran in the opposite door.
Didn’t see me, BR’d him. Headshot.
Was determined to start off Halo 4 with a kill rather than a death. Friend of mine was the first kill of the game, he was disappointed lol.
Arctic BR kill, Haven 
Made me feel good ripping down someone with a precision weapon. I’ve Mastered the thing by now too…good times.
Guys back was turned and i gunned him down on the map Adrift with the BR.
I too was determined to start with a kill. First game was on Abandon, I ran down and grabbed the Scattershot. Happened to kill someone at the bottom or top of the lift, I can’t remember. For the first 3 games of my Halo 4 career I did really really well. I got a 20+ spread in each game. In my 4th game I got my -Yoink- handed to me.
It’s 4AM on release day, I decided to stop playing campaign and try multiplayer,it was BTB on meltdown. I shredded some guy with an AR and Started “victory crouching” while the rest of his team was shooting at me to celebrate my first kill.