The text reads:
"Did you know?
"Vegans live 15 years longer because they aren't invited anywhere fun or dangerous. Instead they stay @ home crying & drinking, being careful not to cry into the drink because tears are a product of animal suffering.
"The more you know..."
However, it turned out that no-one from Windsor Meats wrote the joke; they just copied it directly - without crediting the creator - to sell their product. The joke was actually written by comedian Myq Kaplan. Kaplan, who is vegan himself, performed the joke on Conan O'Brien's TV show in 2012, and in response to this photo, wrote on his blog:
"I haven’t read all the comments and responses, but a running theme seems to be “Vegans and vegetarians don’t have a sense of humor,” coming from people who think the joke was made by a meat-eater at the expense of vegans.
"But I’m the vegan who made the joke. And I can take a joke, I just can’t take that a joke was taken from me. (I mean, I technically CAN take it. I’m strong. From spinach. Like Popeye.)"
He went on to say:
"But I do think that when people create something, other people shouldn’t take it and use it without permission or credit."
Getting permission and giving credit are hugely important, both to the creator whose content you're using, and to the readers of your work. It gives context, and allows people to go back to the original source. While the shop has apologised for using Kaplan's joke without crediting him, even if they had asked for permission to use this joke, it's likely he would have said no.
You can watch Myq Kaplan's bit on Conan here (warning: some adult content).