I missed the joke here.
Is it a play on the letter’s author’s name?
Sorry for being so dense.
In England ‘spud’ is slang for a potato.
Of course Cecil is in the US.
So presumably it’s an affectation (like calling someone ‘mate’, ‘guy’ or ‘bubba’).
I knew spud meant potato, but still…
What? Cecil’s just calling the guy dumb?
OK, run this past one more time, please.
In England, calling someone a POTATO or SPUD is “like calling someone ‘mate’, ‘guy’ or ‘bubba’”?
I’m more confused now than when I started the darn thread.
Calling someone Spud, in the US, while a bit archaic(Hi, Cecil), is usually just like calling them pal or bud just as glee said.
Unless, of course, you’re talking to Mr. Potato Head. 
Spud is very often associated with the name Murphy. So we have" Spud" Murphy. Likewise there is
“Chalky” White
“Dinger” Bell
“Hi” Opal
etc.
I liked that movie War Games, too.
Funny I watched Train Spotting tonight and still missed it.
No, no, no. As Dr. Science (I think he’s Cecil’s cousin or something) tells us, SPUD is an acronym for “Scientifically Produced Ugly Dog”. It looks sort of like a Yorkshire terrier, but it knows it’s ugly and has the good sense to shut up about it instead of yapping like a yorkie does.
Sorry if I wasn’t clear.
I was guessing that Spud was a friendly name for a stranger in the US.
Here in the UK, we use ‘Wotcha mate!’, ‘Yes, guv’, ‘He’s the guvnor’, ‘Hello, big boy’, , ’ Go ahead, duckie’, ‘Excuse me, Sir’ etc.
Ah, that explains Spud McKenzie.