Historically known as "the vagina of the mouth," this area has gained recent popularity among "headventurers" for remaining constantly wet and sensitive.
Headventurer:"Sheila, lets try something new"
Sheila: "oh ya, put it in my undertongue"
1. (n): Area on the bottom of the tongue where the tongue attaches to the rest of the mouth. (You know what i'm talking about- it's all veiny and full of saliva)
Girl: "I was picking my teeth with a toothpick and I slipped and stabbed my undertongue today!"
Guy: "Wow. You impaled your undertongue? Gross."