1. Perineum, ie area of skin directly anterior to the anus. Generally refers to the male version.
2. (Obscure) Unkempt, often awkward character who just doesn't seem to fit with the rest of the group. Unrelated to 1; originated in Cape Breton, Canada, but has spread as far as Australia.
1. Don't forget to wash your grundle.
2. I feel like the family grundle.