Intense sex where the ferocity and often violent nature of the acts performed are the primary aphrodisiacs elevating the intensity of the experience for all persons involved. Substances can increase the potential for Demon Sex by numbing pain receptors and lowering inhibitions.
Aleister Crowley, informal BSDM (formal BSDM risks losing the spontaneity one would assume Demons embrace), screwing to Ministry.
"Seriously, shit got crazy. I didn't know where she got the knife or how a power cord was involved, but they were both used in ways that would make Jesus cry. Demon sex man, demon sex"