A grundy that creeps forward to encompasses the vagina, resulting in a cunt grundy, or "crundy."

When your little sister is has her legs and arms both in the sleeves of her hoodie and running around the house dancing like in the "wow you can really dance" tiktok dance/challenge

A grundy that creeps forward to encompasses the vagina, resulting in a cunt grundy, or "crundy."

Crundies are undies that are crusty from dried up semen usually from masturbation ejaculating into the underwear and leaving it there to dry. Crusty+Undies=Crundies.