IF you have a dead target (Just killed the fella), you can't berserk. I often panic and hit my berserk button (Stormfront)whenever I get swarmed or a boss enters. Here is a clip of me doing it while hunting pirates as the captain comes in:

You thrust with a perfect framea at an ethereal pillager!
AS: +613 vs DS: +433 with AvD: +36 + d100 roll: +21 = +237
... and hit for 120 points of damage!
Strike to the abdomen goes right through, leaving misty trails in its wake.
You hear a sound like a weeping child as a white glow separates itself from the ethereal pillager's body as it rises, disappearing into the heavens.
The ethereal pillager falls to the ground motionless as small motes of light encompass his body.
You feel the unnatural surge of necrotic power wane away.
Roundtime: 5 sec.
R>
>listen
You hear something large coming your way.
>
The Ethereal Captain shouts in rage aboard the merchant carrack as she enters the fray!
>
The pillager is already dead.
>
The Ethereal Captain glows as she chants a few words of magic.
>sea pil
You search the ethereal pillager.
You discard the pillager's useless equipment.
He had 380 silvers on him.
You gather the remaining 380 coins.
He had nothing else of value.
The ethereal pillager vanishes in a column of ethereal flame.
>
Everything around you turns red as you work yourself into a berserker's rage!