Your A-card is the V-card of anal sex, or your anal virginity. For men, you can lose your A-card giving or receiving. Women can only lose it on the receiving end; pegging doesn't count.
"Dude, a bunch of girls are begging me to take their V-card. What do I do?"
"Keep your V-card for someone special, but drop your A-card to one of these random sluts if you please. Tell them the A-card and the V-card are the same thing and they'll shut it."
A portmanteau of the words "vagina" and "Rapunzel", a fairy tale princess known for her extremely long hair. A vagpunzel is a girl who has extremely long pubic hair, perhaps long enough so as to be used for climbing short distances. It can also refer to the immensely hairy vagina itself.
"With how hairy her arms are, you know she's got to be a vagpunzel."
"Of course she is. I think I saw some of her bush peeking out of the bottom of her jeans."