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2.
Someone who sleeps with lots of women, unaware of the fact that he is actually HIV positive.

Someone with AIDS/HIV who intentionally spreads the virus by sleeping with as many people as possible
"I can't believe you never wear a condom you fucking AIDS farmer!"

"What do you mean you never wear a Jonny, you've got HIV, you AIDS farmer!"
by Horse-Birdman January 15, 2012
 
1.
A clever yet honest insult towards gay men.

Implying that they are the ones who spread and harvest AIDS thoughout the world.
Yo, Pat you're such an AIDS Farmer
by The Brockville King December 28, 2011