When the tables are voluntarily turned on heterosexual anal intercourse and the female servicee becomes the servicer for the man. Because most women don't have penises, a strap-on dildo is necessary.
1.
Man: "I really feel like getting fucked in the ass today, but I don't dig that whole gay lifestyle"
Woman: "Okay honey, then I'll strap on L'il Pearl and we'll do some pegging then"
2.
Dutchy: "Jude's wife fucked him in the ass with a dildo! She pegged him! He's gonna take his wife's maiden name!"