That was this historical reference to 51s.
An example quoted from the official wartime history of the 479th Fighter Group that transitioned from P38s to 51s.
"The first pilot to finish his missions this month was Lt. Hoverston, strictly a P38 boy with a distinct dislike for the P51 Spam Can."
Basically implying, mass produced, cheaply made etc
P38 = a nice steak
P51 = er...well.... Spam