I just got them from the in-game cheat menu, but they're not really necessary since it infuriates them at low Trust/Love/Lust levels (all 3 of which can be boosted 2 points by giving a cupcake, a flower, and a drink), and once the girls are in the Horny state, they tend to stay in that state unless you piss them off by trying to skip some steps in the "Hot Services" tree or you try to change their wardrobe before activating the appropriate "Hot Service".