The Loser

The sad trumpet eternally plays for the Loser.

The one the audience likes to laugh at. The Loser is completely oblivious to the fact that they are the Loser, which makes it easier to laugh at them. The Loser almost always gets the short end of the stick, unless the Wiener is involved. The Loser is guaranteed to at least be part of the Main Cast if they aren't the Main.

The Loser, if they go to school, will have a small amount of friends, be picked on by at least one person, almost never score with the opposite sex, have average grades (unless it's a Bad Grades episode), be subpar in sports, and is rarely negatively affected by all of this emotionally for a long time. Note that not any of this is guaranteed — it's only common with Losers.