Stir the soup is a slang phrase that is similar to "toss my salad." It is one person taking it in the ass. They can be male or female receivers. When the guy is done, he pulls out and cums on the others asshole. The guy then proceeds to furiously licking the others asshole, stiring their soup. This phrase comes out of Fairborn, OH.
"I hate you. Go get your soup stirred." or "I love to stir the soup. I could do it every day." or "Why did you stir your mothers soup dude?!" or " I had to stir Stacy's soup dude and damn was it delicious!"