Some students skip class, but then run into the professor on the college campus. American stand-up comedian Emo Phillips made a joke:
 
“I was in ROTC in college. I was walking across campus and my camouflage instructor said, ‘I haven’t seen you in class for six weeks,’ and I replied, ‘I guess it must be working.’”
 
The joke has been cited in print since at least 1997. “Welcome back to invisibility class. It’s pretty disappointing to see so many of you here” is a similar joke.
   
           
Wikipedia: Emo Philips
Emo Philips (born Phil Soltanek; February 7, 1956) is an American comedian. Much of his stand-up comedy makes use of paraprosdokians spoken in a wandering falsetto tone of voice. The confused, childlike delivery of his material produces the intended comic timing in a manner invoking the ‘wisdom of children’ or the idiot savant.
 
Google Groups: rec.humor
Stealth Fighter Crash
GWLucky
9/14/97
(...)
This reminds me of an Emo Phillips’ classic:
 
“I was in ROTC in college.  I was walking across campus and my camouflage instructor said ‘I haven’t seen you in class for six weeks’ and I replied ‘I guess it must be working’.”
     
Google Books
It’s a Man’s World:
800 Jokes from the Guy’s (Warped) Point of View
By Judy Brown
New York, NY: Barnes & Noble Books
2005
Pg. 48:
l was in the ROTC program. l remember once l was walking through campus and my instructor grabs me, and he’s a real big guy, and yells, “lt’s been six weeks since l’ve seen you in camouflage class!” l said, “l’m getting good.”
     
Google Groups: alt.humor.jewish
~.~ 3fer
Renee
6/5/05
(...)
I was in the ROTC program. I remember once,
I was walking through campus
and my instructor grabs me and he’s a real big guy,
and yells, “It’s been six weeks
since I’ve seen you in camouflage class!”
 
I said, “I’m getting good.”
 
Twitter
PV=nRT‏
@HondoLane
One time at Advanced Infantry Training the instructor said ” hey Hondo how come I haven’t seen u at camouflage class” said I’m getting good
7:57 PM - 3 Sep 2009
 
Twitter
Lisa Horstman‏
@lisahorstman
The ROTC instructor said, ‘Emo, it’s been six weeks since I’ve seen you in camouflage class.’ I said, ‘I’m getting good.’ -Emo Philips
10:26 PM - 12 May 2010
 
Twitter
Ian Weaver‏
@iwweaver
When I joined the RAF my Instructor said to me :  I didn’t see you at camouflage training this morning. I said: Thank you very much Sir 😊
10:30 AM - 9 Jun 2011
 
Graphic Joke
Attendance Problem?
January 16, 2014 by grin
Camouflage Instructor: “I haven’t seen you in class for a while.”
Student: “Thanks!”
 
Twitter
McGuire‏
@mcguireonfire
Replying to @dfr10
@dfr10 I was walking through college and my camouflage teacher said I haven’t seen you in class. I’m getting good! #emophillips
1:15 PM - 3 Oct 2015
   
Twitter
Stewart Weir‏
@sweirz
Replying to @ScotsFootyCards
I studied camouflage techniques at college and one day the instructor said “I haven’t seen you in class lately ...”
10:37 AM - 12 Jan 2017