Someone who hijacks class discussion (and hence, class time) with irrelevant, or tangential opinions and/or questions.
Someone who attempts, usually (and repeatedly) failing, to demonstrate his or her intellectual prowess by asking questions "out side the box." These questions, and the answers/discussion they force the professor to entertain, are never tested and rarely add positively to the lecture.
3. Someone who repeatedly asks questions during lectures that would be more appropriately discussed after class.
1. During discussion of a case in criminal law, one notorious law school gunner once proclaimed: "Professor, the holding of this case reminds me of a Klingon proverb, you know, 'Revenge is a dish best served cold.'"
2. A law school gunner would preface a question with, "Well, in the bible it says x." Prof. would answer, "Well in the Constitution it says Y. And it's the Constitution that will be tested on my exam."
After asking a dozen questions in the span of 45 minutes, the following exchange may occur:
Gunner: "Professor, I have another question."
Prof: "Ok, but this is the last one for this lecture, we have to move on."
Gunner: "Well, I have several more, and I'd like to ask them." (The gunner then proceeds to ask them).