That gets a laugh--specifically the mention about being a knight. But he did start this, so he can't be that surprised about it. That's why his smile turns into a grin, his "Sure" the same dulcet tone that Inigo uses.

"Should I say thank you to my prince for feeding me first? --my lord," he thinks to add, last second. Look! He knows how these titles work! "I'll do anything you want me to."

And Inigo can make that into a dare, if he likes.