Less emotion for the characters, they don't just fall madly in love, they fuck because it is fun or convenient and they want to. They don't confess their love to one another as they fuck, more dirty talk less emotional dialogue. Same goes for "bad sex" (eg. rape, drugged sex, hypnotized sex) don't be dramatic, they just want to fuck, they're not evil or anything, just horny. Basically write more "matter-of-fact"/practical/unemotional.