Wiglaf, if she hates you more than Arthur, then calling you mere hired help is hilarious. Seriously, the implication is that you were employed to literally clean up poop for them at bare minimum. He could have conceivably also been one of the people helping to recover the herd of dragons Arthur unleased (mentioned on page 74 / Ch 5 p 8), and since they ARE being kept in stables, you, Wiglaf, were theoretically cleaning up dragon poop.

Basically, everyone around you (except your sister) is imagining you cleaning up a variety of the most noxious forms of poop imaginable every time they say that. And smirking at the thought.

If I was to guess it’s because calling Wiglaf their stable boy is reeeally funny to her?