What's really hot?
A woman giving in to overwhelming pleasure against her will.
The body conquers the mind.
This situation is most easily accomplished through rape, but I much prefer consensual or semi-consensual situations, such as:

• Two couples swap partners, but the woman ends up enjoying the other man way more than intended.
• A woman is pleasured or fucked while trying to focus on some unrelated task like reading the news. At some point she loses her concentration due to the overwhelming pleasure.
• A woman is on some kind of game show and gets pleasured or fucked as a "punishment" for losing.

Unfortunately these situations are relatively rare compared to straightforward rape, and seem to only really exist in Japanese porn.