"If a listener nods his head when you're…

“If a listener nods his head when you’re explaining your program, wake him up” is a jocular one-line saying written by American computer scientist Alan Jay Perlis (1922-1990) in his “Epigrams on Programming,” published in ACM’s SIGPLAN Notices in September 1982. The saying has been popular with computer programmers, but has also been used in business.

Wikipedia: Alan Perlis
Alan Jay Perlis (April 1, 1922 – February 7, 1990) was an American computer scientist known for his pioneering work in programming languages and the first recipient of the Turing Award.

Herbert Klaeren
Epigrams on Programming
Alan J. Perlis
Yale University
This text has been published in SIGPLAN Notices Vol. 17, No. 9, September 1982, pages 7 - 13. I’m offering it here online until ACM stops me.
(...)
17. If a listener nods his head when you’re explaining your program, wake him up.

Google Books
The Coevolution Quarterly
Issues 37-43
1983
Pg. 102:
If a listener nods his head when you’re explaining your program, wake him up.

Google Books
Humour the Computer
Edited by Andrew Davison
Cambridge, MA: MIT Press
1995
Pg. 18:
If a listener nods his head when you’re explaining your program, wake him up.
Alan J. Perlis

Google Books
JavaSpaces Principles, Patterns, and Practice
By Eric Freeman, Susanne Hupfer and Ken Arnold
Reading, MA: Addison-Wesley
1999
Pg. 217:
If a listener nods his head when you ‘re explaining your program, wake him up. — Alan Perlis, Epigrams in Programming

Twitter
Linux Message of Day
‏@linux_motd
If a listener nods his head when you’re explaining your program, wake him up. #Linux
8:00 PM - 2 Nov 2014