"Note to self: Remember meeting with the baron's wife tonight; don't forget to take those potent herbs from the healer! We don't want another incident like last time."
Right idea, not salacious enough.
No no.. Not the barnoness, no no. Now, reminding him that he needs to bribe the baron's stable hand to get unfettered access to the baron's horse-- now THAT's salacious!
In the medieval period, if the King wanted the baron's horse for any reason, he would simply order the Baron to give it to him.
And having sex with a horse is not actually that weird for a medieval king. It would not hurt his reputation that much.
It at least wouldn't effect him that much, since anyone who tries to insult him who isn't the fool will be executed.
You aren't thinking about it the right way. Intrigue is a convoluted, and complicated web of concepts.
1) Yes- the king can demand basically anything, and his subjects are compelled to comply. However, politics is all about image. If a king feels there is nothing wrong whatsoever with being a horse fucker (or being fucked by a horse, as the case may be... I intended this latter), he will be open about it and inform the baron openly that he is a fine judge of horse-flesh, and that he wants the use of the horse for the night.
That is NOT what we are establishing here, with the message.
Firstly, the reminder is to bribe the stable hand; This immediately asserts that the king himself views the act as disfavorable, and something to be concealed. Secondly, it asserts that the king is willing to use covert and illicit means to secure something he finds disfavorable for himself. Thirdly, it asserts that the baron's estate has untrustworthy staff, and that the king is exploiting this to his clandestine advantage, and fourthly, he is doing this knowing full well that the baron will disapprove, and is doing it ANYWAY. (thus showing open disdain for the baron.)
This is in addition to the obvious slight against the king's mental health, by brightly spotlighting that he is so forgetful or mentally infirm that he must remind himself of his clever schemes throughout the day, and that he is so far down that road, that he also must remind himself not to set reminders that others will hear.
Actively seeking a very... unique... form of sexual gratification, and doing so clandestinely, fits neatly with the theme of nascent mental illness (and thus inability to properly rule), much more than more ordinary lust (such as for the baroness.)
That is why it is more salacious.
The danger that the king will then attempt to DENY the now high-gossip topic, will only cement it further that the king is insecure about himself and his ability to govern.
Perversely, this may force the king to openly engage in such practices to re-secure the image that he is a powerful dictator that is secure and proud in his pronouncements, and bold in his actions. (rather than cowardly, by acting through deceit.)
EG-- It might force him to have to go get fucked by the baron's horse to save face.
Which is why it is so much more delicious.