Naughty Naughty is an Achievement in Halo 3: ODST and Halo: The Master Chief Collection. It is awarded for killing 10 Engineers in New Mombasa at night, alone or with another ODST. It is worth 5 Gamerpoints.
If you stumble upon a group of Covenant forces being shielded by an Engineer and do not wish to give away your position by trying to kill the engineer first, you may kill the squad they are shielding and then they will self-destruct. As long as you have hit the Engineer with your weapon sometime during your attack, you will get credit for killing it.