[Bart was listening to Zatanna's explanation intently - cheap subject it might have been, but he actually was curious about it. He doesn't have much experience with non-fictional magic. He misses the sound of Tim's entrance, but he doesn't miss that little dig.
Now he knows that Tim's been there for who knows how much of the conversation, and the flush is just never going to go away. Maybe if he speeds up and gets a bunch of things done in the next five seconds. He could repaint the whole place. Except eventually he'd get bored and wander back into this conversation to find that it hasn't been that long and that Zatanna and Tim are still thinking of his underwear.

His next thought is that he's still small enough that he wouldn't need that large of a rock to crawl under and die.

But the one immediately proceeding is that he's not going down so easily. Bart folds his arms over his chest, jerking a thumb at Tim before tucking his hand under his elbow to cross his arms properly. Anything to look tougher while he waits for the excess blood to drain from his face. ]

You should ask this guy about proper underwear choices. And how to wear leather. Pretty sure he has to coat himself in baby powder to get that monkey suit off and on. Oh. And don't forget to ask about the mesh shirt.

[Who's laughing on the inside now, Birdbrain? Well, that's what Bart thinks to himself. The reality is getting that out in an unembarrassed tone was a struggle. Add his ears and neck to the list of things gone red. ]