DELIVERY and detail have a great deal to do with the success of a joke. ;D
For example, in the joke you quoted it is supposed to be a BABY seal...
Makes all the difference in the world.
Let's try it again...
"So, this BABY SEAL walks into a CLUB!"
It's funny because there's so much controversy about the killing of the small, white, furry creatures.
They must be killed for their beautiful pelts BEFORE they shed and leave the rubbery seal skin. They just walk up to them and POP 'em in the head with a bat (or club).
What????
Still not funny?
Wait til I tell you the one about the car-owning chimpanzee who blows a seal. It's hilarious!!!