This mission is given by Sal Gravina.
"Jimmy! Sal Gravina. I've been hearing that one of Tussle's captains has been mouthing off, saying that my crew don't got what it takes, saying he's gonna take me out, and all the usual kind of bullshit. They call this idiot Dirty Daniel. Fuck knows why. Anyway, I want you to kill him, because I don't take shit from a guy that sounds like a sex pest."
From the mission start, drive about one block south to Dirty Daniel's location. Several Bombers will immediately open fire from a four story apartment building. Once you take them out make your way to the top floor and you will find Daniel in a hallway at the end.
After you kill him you can either go back to your car or simply go on foot to the nearby safe zone to end the mission, keeping in mind that you may still encounter hostile Bombers along the way.