What makes this funnier, to me, is that animators and directors all had discussions about how this scene was going to be drawn. It's not like some rogue illustrator slipped this one in - the studio itself committed to the gag. Plus, it's very in-character for Casey Jones who is rarely seen without that mask, or unarmed.

This also has strong video-game energy, like "Dragonborn wearing a chef's hat", or "Solid Snake in a cardboard box."