Throwaway line
JOKE DELIVERED "IN PASSING" WITHOUT BEING THE PUNCH LINE TO A COMEDY ROUTINE
Throwaway gag; Throwaway joke
In comedy, a throwaway line (also: throwaway joke or throwaway gag) is a joke delivered "in passing" without being the punch line to a comedy routine, part of the [up] to another joke, or (in the context of drama) there to advance a story or develop a character. Throwaway lines are often one-liners, or in-jokes, and often delivered in a deadpan manner.