Hi, there's no difference if what you say or do is in a pm or a public chat--content is moderated across all the spaces on the platform (private is public for support and mods). Also, it would be irrelevant if it were your idea or the user's.
Regarding your question, the short answer is no degrading content at all.
Now, I don't know what exactly would be a "degrading kink" for you, but there are some tags that come to my mind that may be related to what you're thinking of: #slave #cuckold #cei #humiliation #sissy and you already mentioned #sph.
I would think that if the tag is allowed on the site then the related content is allowed too. However, keep in mind that all those are edgier topics that often operate on the borderline of what's permitted. So it could be pretty easy to cross the line even without noticing. Telling him that he has a "small package" is ok, and that "it wouldn't even tickle you" is ok too, but when the tease and fetish become "degradation" or something else that's forbidden is unclear. The best answer you'd get from them is something on the lines of either "it is forbidden" or "it is allowed BUT read the ToS and rules" that ultimately leaves you at the starting place. You can say or do something one day and be ok, and then do the same the next day and be banned because the AI or a particular mod judged it wasn't actually ok after all. See what I'm saying?
So if it's not something that really entices you or something that you're already into, then I'd suggest you avoid it just to stay safe. If you do decide to venture there though, extreme caution is advised, as you will be dealing not just with your words and actions but with the user's too.
Since I noticed you're kinda new, at least on the platform, I'll add a little advice: have your ban button ready. More so for when some user tells you something related to a serious violation like CSAM, scat, pays off platform, etc. As soon as you detect any hint of a prohibited topic, it is expected that you immediately stop any interaction with the user (no further answers at all, like AT ALL), stop the pvt show (if you're in one) and report and ban the user. When in doubt, it's better to ban the user. No tip is worth the risk of losing your room.