Yeah they are better to watch in order but not at all necessary if he just wants to catch reruns.
You couldn't be more wrong. Just in the episode he mentioned, you'd have to know:
- who the blonde guy in space was ordering the hit by the KGB
- Why Ray is in a wheelchair
- Why Cyril sucks as an agent
- What's the joke about Carol being rich
- And most importantly, the 3 seasons prior that cover his Oedipus complex.
Not saying you can't enjoy an episode without watching all 3 seasons, but there's so many running jokes, it would make it much better.