He's trying to be that antagonist that she's clearly craving, but Pete can't help but grin as Lita laughs. It's a nice sound, despite the bitch fit she's having, and it occurs vaguely to him that he wouldn't mind hearing it again. But then the moment's gone and Lita Singh is back to being a royal pain in the ass. Even if she is inviting him to look at her body.
There's so much that he wants to say to her as she waxes poetic about her own attractiveness. Pete wishes he could deny it, but the truth of the matter is that they are quite possibly the most good looking doctors left in the entire human race.
His mind runs through a series of possible responses that range from overly sexual ("Baby, I know you want my gunk all up in your gears") to a little less overtly sexual ("I am so ready for your jelly") and straight up benign ("Oh, I think I could handle this"). But then she references what he guesses they're both trying to ignore -- the Supply Scout Annihilator -- and it's like the air's sucked out of the room and he's stuck there, watching the anxiety hit her.
The thing is, if it were anyone else he'd be moving closer and rubbing her back and stuff, trying to calm her down. But it's Lita Singh, his archnemesis, and he knows the feeling is mutual. She'd probably rather have a zombie give her a hickey than him touch her. So he waits until her eyes open again before he says, "You don't have to explain. I'm just so beautiful, you couldn't look directly at me anymore. I was burning up your eyes like a solar eclipse."