As far as I know there is no such things as stealth in aircrafts. If you are using modern radar then you can spot any aircraft, even those new stealth jet fighters that the US is about to start cranking out.
Stealth capability isn't a boolean property. Intermittent detection isn't enough to target an aircraft. Being able to track from the ground, with numerous antennas and supercomputers, is much easier than tracking from the limited-diameter head of a radar-guided missile.
It isn't really a joke so much as a humorous way to describe a nasty reality.
Having to keep the radar on though-out the missile's entire flight would be a good example of a possibly life-shortening exercise for the sender of the missile.