They aren't laughing at him, except for one person: Cindy. But that is how Cindy rolls and really, if she didn't laugh him, she'd cry at how out of place he looks here with that babyface he and Arthur both share. Cry from laughter, anyway.

Honestly, her first idea was to ignore Rex on account of him not being Arthur, but turning away from her like she didn't see him makes her see him and brings her attention right around to him. He practically puts the spotlight on himself, Cindy thinks with an almost sadistic smile on her face as she slides closer to him to whisper in his ear. "I hope your babysitter has a side job as a dancer and she was called up on short notice. And that's apple juice in a beer bottle."