Soifon actually, is, gay. No surprise there but she's in the closet so far that she'd probably never admit it even to herself. So basically? All her 'relationships' have been with men, regardless of her preference. Shinji would fit into the type that she would 'pretend' to date. Loud, obnoxious and someone she could scare easily into submission.

....I'm afraid it would turn into a "yes, he's a jerk but he's my jerk" type of thing.