To write smut in such a way that it just seems like the writer is projecting their insatiable lust into their work as makeshift porn.
This type of writing smut is characterized by weird, robotic behaviour between the characters as if they were AIs, lack of realism explained in sexual activity (no pre-cum, no optional describing of the hymen breaking if the woman is a virgin and so on), unrealistic behaviour during sexual intercourse between the characters, for example: moaning loudly at the first thrusts, you could maybe pass this off if it were described as the person moaning trying to lie in order to boost the other's confidence, in any other case that isn't mystical and if it's just normal sex, if you've ever felt sexual pleasure before, you know it builds up, going from a nice little warm feeling to an orgasm, depending on how intense the sex is and what gender is receiving the sexual pleasure (men cum more than women, and cum more easily), this smut is also characterized by bad plot, and it leaves a bad taste in any sane reader's mouth.
Sometimes in some smut, random characters join in to the sex just to make it a threesome in this type of smut juat because the writer's horny. Sometimes, women in smut have intercourse with a guy with a massive cock (8 to 13 inches) and they don't even make it seem like it hurts when the guy goes all out, and in realistic smut, that would be, aside from the sexual enjoyment of sex, pretty painful.
Here's an example of blanksmutting:
Jessica and James entered the bedroom right after getting home from getting married (gotta keep this halal brah frfr). James immediately noticed Jessica's BIG BOOBIES and got super hard. Jessica immediately noticed this, and took his boxers off. Then they had HOT sex!!! (keep in mind, both of these people are virgins who never had a single second of sex in their lives before)
Jessica got down to her knees and starting deepthroating James like a proffesional.
Then somebody barged into their rooms, it was Bartholomew, a big black oiled up man who's a registered sex offender. "I'm gonna suck your BIG FAT BBC COCK, James!!!"
And then they got airstriked and died. The End.