I don't know the origin. The phrase is a way of saying, "Something bad happened to me, but worse things have happened to other people." Example: A man is in a fight in a bar. After the fight, he has bruises and a bloody nose. He says, "You should see the other guy," which means the other person in the fight is in an even worse condition. The phrase can be used humorously: You stand on a chair to change a light bulb. You fall off the chair and hurt yourself. People come to help you. You say, "You should have seen the other guy." There is really no "other guy." But you say this just for the sake of injecting a little humor into the situation.

An expression usually used to indicate that you had a better outcome from an event than another person did. Example event: You were in a fight. Someone says to you that you look bad from the fight. You reply: "You should see the other guy"

The phrase is used to reference the condition of your opponent after you beat them in a fight, often used by someone who is injured, in an often humorous manner. It is like saying, "Yes I am hurt, but I hurt the other guy worse."