A Valentine’s Day joke is:
 
GIRL: I can’t be your valentine for medical reasons.
BOY: Really?
GIRL: Yeah, you make me sick!
 
The joke has been cited in print since at least 1999.
   
 
14 February 1999, The Sunday Times of India (New Delhi, India), “Gag Bag,” pg. 24, col. 7:
Liz : I can’t be your valentine for medical reasons.
Jon: Really?
Liz: Yeah, you make me sick.
     
Google Groups: alt.humor.puns
Weakly Jest For Kids 03-02-04
Stan Kegel
3/2/04
(...)
“I can’t be your valentine for medical reasons.” “Really?” “Yeah, you make me sick!” (Jill K.)
 
Google Groups: alt.humor.puns
Kids Puns of the Weak 0-15-05
Stan Kegel
2/15/05
(...)
“I can’t be your valentine for medical reasons.”
“Really?”
“Yeah, you make me sick!”
 
Google Groups: Clean Humor
Valentine’s Day Oneliners
KB
2/13/08
(...)
Liz: “I can’t be your valentine for medical reasons.”
Jon: “Really?”
Liz: “Yeah, you make me sick!”
 
Twitter
Bo
‏@twitterbo
Jane: “I can’t be your valentine for medical reasons.”...Dick: “Really?”...Jane: “Yeah, you make me sick!”...8-)
12:01 PM - 14 Feb 2009
 
Facebook
Funny jokes
February 11, 2014 ·
Girl: “I can’t be your valentine for medical reasons.” Boy: “Really?” Girl: “Yeah, you make me sick!”
     
International Business Times
Valentine’s Day Jokes: 15 Funny One-Liners To Make Singles, Kids And More Laugh On Feb. 14
BY PHILIP ROSS @THISISPRO ON 02/10/15 AT 11:06 AM
(...)
1. From jokes4us.com:
Girl: I can’t be your Valentine for medical reasons.
Boy: Really?
Girl: Yeah, you make me sick!
 
My Town Tutors
Valentine’s Day Jokes: Top 25 Valentines Day Jokes
Posted on February 12, 2015 by mmolloy
(...)
8. “I can’t be your Valentine for medical reasons.”…“Really?”… “Yeah, you make me sick!”
 
Google Books
Wimpy Kid Jokes About Love & Valentines!:
The Ultimate Book of Valentines Jokes, Riddles, Fun Trivia, Facts, Puns and More!
By Marcus Stuart
LOL Kids Books
2016
Pg. ?:
“I can’t be your valentine for medical reasons.”
“Really?”
“Yeah, you make me sick!”