What saying of Bear's vexed/confused Crispin the most?

Crispin is referring to Bear's saying that every man should be master of himself. Bear is a fiercely independent character, certainly a good deal more independent than most people in medieval England. Society at that time was very rigid; the class you were born into was likely to be the class in which you died. Everyone was supposed to know their place in the social pecking order, fulfilling their own specific function. The class system was sanctified by the Church, which believed that it had been ordained by God.
Crispin shares the prevailing ideas of society in relation to class. He's always believed that God appointed everyone to their station in life. Everyone has their own place and function in this world—lords to rule and fight; clergy to pray; and everyone else to toil, serving their earthly masters and their God. Crispin's still quite young and naive, and so has never questioned the existing class system. So when he comes across someone like Bear, who asserts his independence against what he regards as the divine order of things, it's not surprising that he should get rather cross about it.