Abstract term for an extremely painful orgasm. More an overload of the senses, and an acutely powerful feeling of its own, than an amalagamation of other sensations. Although it involves extreme aggression, it is nonetheless often a pleasurable, even purifying, experience.
Though derived from 'imperial' + 'orgasm', it has come to signify the subjection to a more animalistic or butchering rage which purges itself in an immense outburst of sexual desire or frustration.
A: "I'm going to tell your mother that you smoke crack."
B: "Fuck off, or i'll give you a fucking imperiasm!"
A: "Have you heard of a band called Meshuggah?"
B: "Yes! They are fucking imperiasmic!"