Actually, she's kind of a bitch.
It used to annoy him and it has made her fairly unpopular around the office, but bizarrely, he finds himself looking forward to her catty comments, barely veiled insults and blalant lies.
He actually kind of respects her for it. She doesn't fear retribution, she makes it impossible to get any crap past her and she certainly isn't lacking in wit. It'd be nice if she showed some self-preservation instincts when dealing with super villains, but if she cowered at the sight of an idiot in a stupid costume, she wouldn't be Pepper.