There's lots of fic out there with humans being fascinated and turned on by tiefling horns, tails and such, and I love it, but it'd also be really fun to see that dynamic reversed, with the tiefling partner being curious and horny about human anatomy. Playing with their partner's hair and stroking the smooth curves of their skull, subconsciously expecting their fingers to bump into horns ... groping their ass or resting their hand on the small of their back and they keep being drawn to the little divot at the top of the butt where a tail should be ... being amazed how easily their tongue slips into their mouth while kissing because oh yeah, they've just got those cute little blunt teeth ... you get it.