Malo is the little child who resembles an infant or toddler, but is in fact probably one of the smartest children in Hyrule. He tends to make fun of everyone he encounters. Here is how to get him to make some of his comments:
When you are showing everyone how to use the sword and the slingshot listen to Malo's response.
When you find him in Kakariko Village, enter his shop and he will say rude things to you.
When you are showing off your archery skills to the children, cancel. He will ask if you need more arrows. Say "No" and he will ask if you want to give up. Select "I am no quitter". He will then quickly respond with some snide comment about how slow you are.
After the store is closed in Kakariko Village, come back at certain times of the night. Before morning, he will leave comments on his door.