Non Sequitur

Non sequitur occurs in speech when someone says something completely random. It is a statement that is in no way associated to the previous subject. This happens in a conversation when someone interjects an off topic comment.

Sue: "How was your fishing trip?"
Dave: "Monkey banana."

It is used in comedy and is the name of a comic strip. In logic it is the result of an argument that does not adhere to its context. The etymology of non sequitur is from the Latin meaning "it does not follow."