A transparency and a lecture using transparencies. (No relation to the advice.)
Our bad, worse and worst advice corner
Bad – When you give a talk with transparencies or computer presentations, don’t go over the content of the transparencies but rather assume that the audience reads and digests them while you develop the matter even further and make comments about their content.
Worse – The same as above, except that the transparencies are very dense and technical and hard to understand.
Worst – The same as above except that the transparencies are handwritten in an unreadable way.
Answer to Trivia question:
Q: What do Yehuda Agnon, Michael Ben-Or, Ehud Lehrer, Uzi Segal (whose calibration theorem was mentioned in the post on the controversy around expected utility theory), Mike Werman, myself, and quite a few others, all have in common?
Hint:
Answer: We all, (and altogether more than 20 students) took part in Benjy Weiss’s mathematics course for high-school students in 1970/1. The picture is of Weiss and his Ph. D. supervisor William Feller in Princeton. From Jay Goldman’s photo album. About twenty years later I gave a similar course to six high-school students, 3 Assafs, 1 Matan, 1 Tomer and 1 Elon.
Combinatorics and more 
Dear Prof. Kalai,
This list of students was inspiring to look at, and reminded me of Doron Zeilberger’s post on Israeli math training on the occasion of Noga Alon’s 50th birthday. Off-topic, I would like to remind you of something amusing that happened the first time we met. I was an IAS/DIMACS postdoc and was working with Mike Saks in Mike’s office (in 1994); you dropped by and asked if I was a mathematician or CS person, and I answered “the latter”. That same afternoon, I spilled coffee all over myself at a DIMACS coffee break, and Mike promptly pointed out the stereotype that it is mathematicians who do this more often than computer scientists ..
Dear Aravind, many thanks for your comment. Let me respond by an even more off-topic story. Once in the mid 80s, I went to visit Mike but somehow I could not find his house. So I asked somebody on the street if he know were Mike Saks lives. “Do you want troubles?” the person replied. I did not understand and reapeted my question. He got angrier and asked me how this Mike looks like. Well, I said, he has a redish hair and a beard and he is rather tall. The person was ready to burst: “I have a red hair and I have a beard and my name is Mike and now tell me why you call me names? Do you want troubles?” Then his mother came down and I assured them both that he is not the Mike I am looking for, (I think I said something like “the Mike I am looking for is a mathematician”; it could have been taken as a terrible new insult; but rather it helped somehow.) and finally I did find the right appartment.