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1.
A vehicle lacking proper air conditioner function. Typically, a jalopy, or otherwise embarrassingly mal-conditioned vehicle. The result of riding in said vehicle is the dreaded sweatback, or sweaty back syndrome.
Bill drinks a gallon of gatorade and takes off his shirt before driving home in his sweatback.
by Jraczkow April 11, 2007
 
2.
(n.)- A racist, derrogatory, offensive term used to describe of person of Mexican or El Salvadorian descent. Sweat meaning getting there back wet and sweaty working in the fields, coining the term "sweatback."
Dylan tried to shank us when we called him a sweatback.
by Maximus Bluntoff April 08, 2006
 
3.
Crossfit cultist or other fitness obsessives that show up in restaurants or grocery stores wearing their sweaty gym clothes.
There must be a gym nearby, this Whole Foods is full of sweatbacks.
by heartajack March 28, 2014
 
4.
Sweatbacks are people who are out jogging or cycling on the road. They are in the way and apparently want to work out in front of people just to be noticed.
"Did you see that sweatback? I have never seen loose spandex before!"
by Kimsky June 12, 2011