My personal theory on charm and love spells in fiction are that they force the person to ignore things they dislike about "their lover" and focus only on what they DO like, and/or intense feelings of attraction without any real focus. I like Eve's silky voice, use of constant innuendo, and curves. I dislike her face tattoos, and the fact that she's a demon who's going to flay me alive when we're done. A love potion with her as the focus would fill any part of my mind not thinking about the voice, innuendo and curves with lust and/or thoughts about how great she is. etc etc. Assuming your mind wasn't utterly destroyed in an attempt to make you like someone you wouldn't normally be attracted to (there's a horror story somewhere in there) you would probably focus on whatever more masculine features she had. Her musculature, perhaps, or maybe you'd suddenly find you had a thing for scrawny people. If not, you'd probably just be immune.
Charms like Eve's/Ahri's, otoh, seem too effective for such an immunity or unfocused lust to be the case. They immediately cause the target to move straight towards them without a care in the world for their own safety or surroundings, and as we saw in Ahri's old color story the men she hits with it are driven near-mad. This charm applies across the board, even to creatures like Morde or Thresh that shouldn't feel such emotions. A lot of that is for gameplay purposes, admittedly, but it's all we really have to go on. Eve doesn't seem to care who she makes suffer (judging from her voice lines she DOES prefer men, but her priority is clearly the pain). I imagine she just induces intense lust for her in whoever she targets. "I want my penis in her vagina" is not a feeling a homosexual man normally has, and so it would affect you more than a heterosexual man (to be fair, this logic also applies to hetero male virgins). You'd have your hands on her before you even realized what was happening, and then she'd kill you.
Feeling skeevy yet? No? Cuz if I'm right it gets worse if the person is a lesbian. Kind of the problem with charms/love spells, they get REALLY creepy if you think about them too hard.
