This is a term used for defining a poorly made joke, typically a racist, or sexual innuendo which brings absolutely zero amusement to the listeners. The best way to deal with such a joke is to either ignore it or call the wannabe comedian a tool and shake your head.
While playing halo you are on the yellow team and you are playing against the brown team. When suddenly one of your teammates shouts out "Hey I just killed two brown people!" This is a perfect example of the unintentional Schauermann joke. Be Wary. DO NOT ENCOURAGE. A Schauermann Joke is very contagious and if it is not slapped down in the bud it will spread.