Bizarro Episode: "Discovered in a Graveyard" - Doyle is in a coma and has an entire episode's worth of weird, disjointed memories/dreams. It is something of a marmite episode.
Ending Fatigue: Averted; things were typically wrapped up quickly after the bad guy had been caught, or objective achieved. In many cases that was the final scene, with just a few words of post-action dialogue or banter before they went straight into the end credits.
Fanon: The Professionals has quite an impressive array of fanon, including:
The reason the sets are always different for Bodie and Doyle's respective flats every time we see them is that CI5 maintains a number of flats which it's agents live in, and they move their agents around regularly.
Doyle is moody, inclined to tears, and a vegetarian.
Bodie is a cold-blooded loner, had a terrible childhood, had a hellish experience being a mercenary in Africa, was rescued from it by Cowley and therefore looks up to Cowley as a father figure. He also has a pretty sophisticated Sweet Tooth (courtesy of said childhood-either he grew into money but hated it or he grew poor and he's compensating).
Ho Yay: Yes, and by the bucket. Modern day fans of the series often have discovered it via old slash zines.
Special Effects Failure: In "Stakeout", a car goes off a cliff in Slow Motion, giving a perfect view of the two crash test dummies in the front seat. Even if a short-sighted audience member was fooled, a dummy head falls off for no apparent reason.
Values Dissonance: The series' violence and fast driving was highly criticised at the time; later on its sexism.