Ok, i am happy that i could at least clear something up. I think i understood your question but my answer was not good enough, so let me try again. This time i will try to show you the programing behind some of this.
Like
quiboune said, the sissy clothing definitely spawns repeatedly after the male character (further known as MC) looses his anal virginity before he gets to lose his "regular" virginity. This is a fact, which is checked as a boolean. If the condition MC_lost_anal_virginity_first is true, the rng is modified therefore, that sissy stuff is definetly spawned onto the MC as a result - if you want you can call this occuring scenario a quest. At that moment where you lose your anal virginity, the type of clothing that you used is definitely not important anymore - that was my misconception after running some tests. I assumed that the sissy clothing quest would only occure after a sufficient high femininity value AND loosing his anal virginity. But, as it is proven, there are currently two ways to aquire sissy clothing. One way would be - like i mentioned earlier, to rise the femininity value above a certain number so that the probability is risen sufficiently; the other is to lose his anal virginity first.
Or to answer the question, avoid losing your anal virginity at every cost before you lost your regular one AND keep an eye on the things your MC is and was currently wearing. Thats the only way to avoid the sissy (clothing) quest. No big magic here since it is just a hiden condition that mainly triggers the quest.
In my playtroughs i never lost my anal virginity first, so yeah, thank you all for opening my eyes on this one.
Not sure, just a thought that came up while writing this, but what happens if the MC can insert a dildo or something like that in his ass - is the condition then met?
- if yes, then that means that you will also have to avoid running bare assed around because of some hidden dildo traps.
- if no, then you probably have a better chance at defending yourself, because npcs prefer targeting not occupied zones first in their rng assesement. So if you run around with a plastic dick up your ass, you won't become a sissy. Actually that would be hilarious, using a fake dick to defend himself from the great gayness.