Inside Out

Q: Dear 100 Hour Board:
Apparently, that is some sort of really cool inside joke, Scoreboards. [In reference to the post "Pedal Your Way to Taxes")
Which leads to the question, how do inside jokes differ from any other jokes? Just because two people know it rather than 3 or more?Please explain to me the difference.
Sincerely,
The Butt

A: Dear Butt of the Joke

Inside jokes are not numerically specified. In-jokes are only identified by requiring a priori information in order to understand the humor. The group sizes can be large (although at least must be one less than the number of people on earth to be designated an 'inside joke'. Unless of course all living people have an in-joke, excluding all the dead or unborn ones. But that seems unlikely). Groups include; friends, family, frats, clubs, professions, races, communities, businesses, aficionados, and so on.
That you aren't in the know on these jokes just demonstrates the horribly lonely life you must lead. Just remember, they are not laughing with you, they are laughing at you. I suppose you could even have an inside joke with yourself - or with someone like Gwitter.
And no, the scoreboard joke was not an in-joke, just required mental acuity.
I offer you several examples of inside jokes:

A physicist, a mathematician, and an engineer are sitting around and one of them says "It says here that Professor X has come up with a new theorem that all odd numbers greater than 2 are prime". Each person present thinks to himself:
Mathematician: 3 is prime, 5 is prime, 7 is prime, the rest follows by Mathematical induction.
Physicist: 3 is prime, 5 is prime, 7 is prime, 9 is an experimental error, 11 is prime...
Engineer: 3 is prime, 5 is prime, 7 is prime, 9 is approximately prime, 11 is prime, 13 is prime ...
Mechanical engineer: 3 is prime, 4 is prime, 5 is prime, 6 is prime...
Computer engineer: 3 is prime, 5 is prime, 7 is prime, 7 is prime, 7 is prime...

or

A mathematician, a biologist and a physicist are sitting in a street café watching people entering and leaving the house on the other side of the street. First they see two people going into the house. Time passes. After a while they notice three persons coming out of the house. The physicist says, "The measurement wasn't accurate." The biologist says, "They must have reproduced." The mathematician says, "If one more person enters the house then it will be empty."

Now these are highly dependent on your scientific foreknowledge. I'll let you decipher them. But I think they're funny. (Especially the computer engineer... :) )

Or one of my favorite is Isaac Asimov's work on tiotimoline, that is so soluble in water, it actually dissolves 1.12 seconds before it comes in contact with it. (Because of the 2 carbon atoms that project into the future and into the past). But I save that for a different post.
Oh and if you don't like this post you can go hopscotch with a camel (you'd get that if you only knew).
Best Regards,
100 Hour Board