I don't know that this accomplishes the much debated task of making Bards cool, but it basically turns them into 4e Warlords and those guys were cool. The prototypical Killscreamer is probably someone from a Mad Max movie like the Doof or the announcer guy from Thunderdome.
Beginning at 3rd level, you may sacrifice a Spell Slot in order to regain a spent die of Bardic Inspiration. The level of Spell Slot sacrificed determines how many spent Bardic Inspiration uses are recovered, up to 5 Bardic Inspiration dice for a level 5 Spell Slot.
Additionally, if a use of Bardic Inspiration is used and, as a result, a creature is killed, that use of Bardic Inspiration is not expended.
Starting at 3rd level, you may add your Charisma Bonus to your Armor Class instead of your Dexterity Bonus. There is no maximum Charisma Bonus which may be applied in this way, as with Dexterity bonuses on some armors. However, if you take advantage of this feature, you are so loud (and are dressed even louder) that you have Disadvantage on Stealth checks.
At 6th level, you may use your Action to allow another character to Attack or Cast a Spell. This does not count as that character using their Reaction, since it uses your Actions, and they may still make their Reaction as normal this round. You may still move but cannot perform any Bonus Actions allowed you.
At 14th level, on each of your turns, you use a Bonus Action to allow another character to Disengage or Dash. This does not use their normal Reaction and they can still React normally this round. Characters may only benefit from the opportunity to Disengage or Dash if it positions them closer to an enemy.