Also known as a
running gag.
A
good running
gag should be
a joke that was
kind of funny the first time, but
one that gets progressively worse as it's repeated. Eventually, you will achieve a
break-point where the joke magically becomes
funnier than the first instance when it was told. At this point, caution should be exercised, because the joke will rapidly deteriorate.
IMHO
The Muppet Show used to have the best running gags.