What is a word that defines a person who adds to a topic or conversation needlessly?

Specifically, let’s say that I provide some information to you about anything. A friend adds their opinion (I’m not looking for opinionated) in the form of a joke that is supposed to be both funny and sarcastic, but it isn’t. Some of you right now may feel compelled to do this in answering this question. I don’t know a word or phrase that describes such a person or act accurately. An example can be, “I bought underwear that have candy cane patterns.” A friend or even stranger replies, “you must really like Christmas or you’re a liberal hippie.” Or something to that effect. People do this all the time. It’s the kind of person you find on facebook or here on fluther “exercising their humor.”

One last thing, the comment doesn’t have to be funny, it can be annoying.