Well according to Niki in Ariadne, it seems Rinne has some sort of thing about sadomasochism. He also got a kick out of humiliating Niki by trying to get him to publicly strip in the original script of Night Club. Got flirty again in an Idol Story with Niki where he straight up said he was getting turned on by looking at Niki's nape. In that regard, Rinne must be one of the few Enstars characters where we factually know one of his fetishes because he has announced it lol. The back of the neck is a vulnerable spot. Furthermore, Rinne is often depicted in artwork as looking down on the viewer with a pleased expression. Don't forget he was the leader of the Leather Harness Shuffle Unit. I think they might be trying to tell us something about Rinne! (he's a sadistic dom, or Do-S as we say in Japanese lol)
Some of this stuff can be seen as part of Rinne's "Bad Boy" shtick but we've seen this behavior typically pops up when he's with Niki, who knows the real him and seems to believe that Rinne is a sexual sadist. So I'd say Rinne is quite Freaky.
This is all I have to say on the subject.