Bernard, Blake, Barrel, Harold, Korg and Feliar. Those are that I've encountered so far..
Xer also has a Love Potion interaction. Do all those other interactions give negative likes? I would imagine Bernard would have a negative one. Don't know about the rest.
Xer has a positive outcome though (and a kinky one at that since I think he is immune) provided you admit to him that you did give him love potion.