Yeah I'm pissed but I would rather take this energy and stash it in a can
Come back and whip your ass with it again

from Eminem – On Fire Lyrics on Rap Genius

Meaning

A reference to the popular, but dated saying “open up a can of whoop ass”, meaning to beat someone up

whoopassi

Along with that, he’s also referencing his song Soldier, specifically these lines:

It’s actually better cause instead of you murderin'
You can hurt ‘em and come back again and kick dirt at 'em
It’s like pourin’ salt in the wounds

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