Any food that has gone bad/spoiled and has an offensive odor. Especially raw chicken, fish, mayonaise, etc. Could also refer to clothes left in the washer way too long.
Grandmother: "Something smells rotten in the fridge. I believe the chicken has gone wang wang. Sniff that fish and see if it smells wang wang."
Toby: "My shirt smells wang wang. How long did it stay in the washer?"