When a male figure takes his ballsack and plunges it into the depths of the female's meat oven while the women is holding her vagina open in the spread eagle position. After entry the guy's balls become glazed over with the female's self-lubricating juices thus looking like swedish meatballs.
Swedish meatballs are meatballs that are covered in a whitish-clear sauce that is very tasty.
During or after anal sex, when the giver of anal sex ejaculates on the feces inside of his partner's anus after cumming, covering them in santorum. Especially when the feces are round, causing them to look like the famous dish.
My girlfriend was incredulous when I told her that Swedish Meatballs don't bother me at all--but I guess they bother her, because she still wouldn't let me put it in her butt last night.