How to have two sims hate each other, but scorching woohoo life?

I suppose you could put them in a room with a bunch of flirty aura stuff. Get them to both have steamy showers, watch romantic tv, that sort of thing. Have them both with the romantic aspiration. If you're controlling both sims try the 'light' romance stuff first back and forth. Problem is, since you want them to hate each-other, if the romance stuff does work, it will also put up the friendship bar too. Hmm...