"A pessimist's blood type is always…

“A pessimist’s blood type is always B-negative” is a jocular one-line saying that has been printed on many images. The saying was posted to the newsgroup alt.callahans on March 11, 2000, when it was credited to the website Pun of the Day.

Google Groups: alt.callahans
Puns of the Weak: 3-10-00
Stan Kegel
3/11/00
(...)
A pessimist’s blood type is always b-negative. (Pun of the Day)

28 May 2000, Arizona Daily Star (Tucson, AZ), pg. F3, col. 4:
Answer to May 28 Cryptoquip:
MEDICAL INVESTIGATIONS HAVE RECENTLY PROVEN THAT A PESSIMIST’S BLOOD TYPE IS B NEGATIVE.

Google Groups: alt.humor
Puns of the Weak: 04/05/02
Stan Kegel
4/6/02
(...)
A pessimist’s blood type is always b-negative. (Douglas Helsel)

Google Books
10 Secrets to Acing Any High School Test
By Lee Wherry,Brainerd andRicki Winegardner
New York, NY: LearningExpress
2003
Pg. 125:
A pessimist’s blood type is always B negative.

Twitter
MrGMc
‏@MrGMc
A joke, and a thought - A pessimist’s blood type is always b-negative. Is it possible to believe and be a pessimist?
8:23 AM - 16 Sep 2008

Google Books
A Man Walks Into a Bar 3
By Jonathan Swan
London: Ebury Publishing
2010
Pg. 221:
A pessimist’s blood type is always b-negative.

Google Books
All Kinds of Humor:
Jokes, Quips, and Fun Stuff for Many Occasions ..., Book 2
By Frank Verano
Xlibris Corporation (Xlibris.com)
2012
Pg. 209:
A pessimist’s blood type is always b-negative.

Google Books
Once Apun A Time:
A Rich, Historical and Sometimes Earthy Collection of Puns
By Robin Leech
Victoria, BC: FriesenPress
2015
Pg. ?:
A pessimist’s blood type is always B-negative.