I've seen this brought up on tumblr, and I hadn't thought of it before!
In Mystery Spot, Sam order pancakes on the first day...
DEAN
Yes. I'll have the special, side of bacon and a coffee.
SAM
Make it two coffees and a short stack.
But after that, he doesn't order anything.
DEAN
Yes, I'll have the special, side of bacon and a coffee.
SAM
Uh, nothing for me, thanks.
and....
SAM
He'll take the special, side of bacon, coffee, black. Nothing for me, thanks.
And then Dean mentions pancakes (and Sam not ordering them) in ep 12.18.
darlingcap