Anyone else might actually react to this in a less uncaring fashion, buuut it's Childermass. He just quirks an eyebrow at Miko's accusatory paw (at least, he assumes that's what she's attempting, but who even knows).

"I imagine he didn't want to admit getting too drunk to drive home and having to sleeping it off," is the overwhelmingly dull answer she gets. "Though he did borrow a sweater of mine the next day. His... really needed a wash."

And what that means, he leaves for her to decide herself. It could be hungover Lambert puked all over himself, could be he spilled coffee on it, could be just about anything.