Was it just lewd because Ruby was getting her hands all lotioned up, or did Ruby stick her middle and ring fingers together? I can't tell.
...I also can't tell if Ruby was just being devious from the start, or if Ruby's intentions were initially innocent but then Yoshiko called her a pervert and she was suddenly like "Ohoho, so she saw it THAT way, huh?..." but I think that confusion was a bit more intentional.