The Sympathy/Pity Con: An attempt to appeal to the other person's compassion to get the other person to give in. Common in children, but also used by adults, an example would be: "All my friends get to stay out late and they make fun of me so can I...". If you have kids you know this one.
The Common Sense Con: What does it mean when someone says: "Well, it's common sense, you know"? Usually it means they don't know how to support their position, so they fall back to this completely empty statement. What's common sense (or obvious) is subjective. The "con" here is that the person saying this hopes the other person will be intimidated by this or think themselves stupid. It almost never works but it sure creates anger.