A person that is slow to catch on to an idea or the punchline of a joke
Derived from the idea of E4+1 showing programs an hour later then E4
A: A brain walks into a bar and asks for a pint, the bartender says i can't serve you, you're out of your head!
B: I don't get it...
(time and a bit later...)
B: Oh i get it now!
A: OMG, what an E4+1