Given the option, when your significant other prefers a family member's company to spending time with you (typically holiday or other family time).
The crock pot serves as reference to all things domestic, familial, and unsexy that occur which challenge your romance with your significant other.
NOTICE: Sexiness/utility of crockpot in actual reference may strengthen, weaken, or otherwise alter the effect of this joke, i.e. an old curbside filth-ring layered crockpot may breed disgust and contempt for your significant other's choice, while a sleek top of the line ionic self materializing crockpot may cause your P1 to either
(a) fail to sympathize with your crockblocked status OR (b) hang up the phone to go buy a comparable crockpot.
P1: " You're free tonight? I thought you flew down with Francis?!"
YOU: " I did, but Mama Dukes said Francis could the learn the family gumbo recipe, so I'm free."
P1: " Your old lady leads the parish in Crockblocking, but that IS some good gumbo."