Sub_Level
wants to fuck an Asian grill.
I haven't used it yet but it seems to be one-time use only? Two if you have two equipped.
Black Hat is admittedly more beneficial to those who go positive closer to 1:1 K/D than >1:1 K/D but yes it's one-time use only.
Black Hat will push those with more deaths to higher overall scores than those with less deaths. If you insist on staying alive, though (let's say you're a sniper in Domination who hangs back and controls parts of the map) you can use Scavenger.