Whippin' 'nades since aught-2
It came from above: in co-op, bail out of a banhee into the passenger or gunner seat of a moving warthog.
Drive by: score a kill from the passenger seat of a warthog.
Me and my rifle: Complete The Library without picking up the the shotgun or rocket launcher.
You're one ugly...: Stick a stealth elite on legendary
Impatience: Clear one side of a covenant dropship before it lands.