Odyssey has posted a formula for determining when a speaker should be placed on the "Never invite again. Ever" list and I agree with all of the points listed for the PISSOFF metric posted there. I suggested switching to a seminar format that resembled The Gong Show and I think there is some real merit here. Just like the show, three judges could be assigned to man the gong and if it turned out that the speaker was horrible, why listen to a full 50 minutes (or longer, ugh) of garbage when you could have the satisfaction of gonging someone and going off to do all of the things you need to? It would also function as feedback to the presenter that they need to work on their presentation skills. It's a win win. Of course, the more I started thinking about this, the more applications to other parts of this job became apparent.
Faculty meetings immediately jump to mind: long tangent that is wasting everyone's time. Gong! An unprepared committee member decides to read the minutes from the committee's last meeting rather than summarizing the key points. Gong!
Thesis defenses / proposal defenses.
Undergrads relating a long story as an excuse for missing class/assignment/exam.
Colleague hovering around to criticize your teaching or research for no reason (The official term for this would have to be the PiT Gong).
Deadwood lab putting in a request for yet another departmental TAship (a whole post for another time).
I'm sure I will come up with more and that you have suggestions, but this could revolutionize my life. Maybe after I have tenure.