Must confess I was envisioning it as the guy on top, pushing in, so yeah, was considering him a rapist. However,the reverse can be true too, she pushing herself onto him. Now, if you want to thicken the plot, you could have them both the inadvertent recipients of a date-rape drug (or equivalent), one that was intended for another party that slipped into both of their drinks. And if the effects run off, they remember more and more of the night as time progresses? (BTW, Love potion works here too.)