Zuko gets flustered when Sokka grabs onto him like that. He blushes deeply and even leans away a little bit out of pure awkwardness. All that is replaced by anger after Sokka says he's "always" this way. He yanks away from the water tribe teen's affections.

"What're you talking about?! Always like what?!" He snaps, a light flush still under his eyes. Just as bitter, he turns back to Dave.

"It's Zuko."