There are some good ones.
I remember one that said, “I’m pregnant!”
On the inside it said, “Just wanted to give you a real good scare for Halloween!”
If a card has a baby, toddler, or clothes-wearing animal on the front, that guarantees it won’t be funny. If the animal isn’t wearing clothes, there’s only an 85% chance it won’t be funny.
People give cards for Halloween? 
I love funny cards, but good ones seem to be harder to find these days. It could be that I’ve read them all too many times, or it could be that my sense of humour has matured over the years (not bloody likely :D). It helps that I’m a fan of stupid puns.
I tend to shop online at sites where you can change the wording as well as choose the image, and if the joke is particularly weak I’ll add my own inside.
Whenever I want to find a good card I go to Evangelines in Old-Town Sacramento. That’s the same place I found a refrigerator magnet for my mom that said: “I FOUND JESUS! He was behind the sofa the whole time!” Many of their cards have a similarly odd, and to me, appealing, sense of humor.
I know the licensing must be steep, but bring back Gary Larson Farside cards. Those were guaranteed to be a cut above the normal greeting card dreck.
I’ve been known to do something like that - I’ll buy a little kids birthday card and change the age. Like if it’s someone’s 35th birthday, I’ll get a 5th birthday card and just write in the 3. They’re usually very colorful and patronizing in a way that I can’t quite describe.
For my college graduation, my older brother gave me a Happy Bat Mitzvah card.
This is brilliant. I love it.