Dean would be the first to say he wouldn't even notice if Lena wasn't completely put together, but he would. He'd probably even ask after it only because it would be unusual and he worried. He didn't care one way or another, not anymore, how she was dressed but he did see it.
He waited until she was settled before sitting beside her, didn't pause to think about it before draping his arm over the bench behind her. "You're missing out not putting bacon on them," he noted, but had no other complaints before accepting the half burger and enjoying a big bite. He never had any serious complaints about burgers, could live off the worst of them. Had lived off them, actually. Burgers were easy and available no matter what kind of town they'd been passing through. "But you've got pretty good taste."
Said in such a way as to imply he meant more than just burgers.