So, I finally got around to playing RPG mod again, and in my second play through, I found the hidden sex scene. (Yoshi, you perv.
) There's nothing explicit though - It was pretty funny actually.
To unlock the sex scene, take the sexy perfume from the abandoned farm and equip it. After that, certain NPCs of the opposite gender will take you to the back room
if you talk to them. (There's nothing explicit, don't worry)