Yikes. I’m the most ff-happy using Waystalker with Swift Bow, and I’ve gotten ~150 at worst (and that was the first game on her on a bad day), usually “only” 40-60, and even that feels like a lot.
AoE weapons (Hagbane, Fireball, to a lesser extent Conflag, Blunderbuss and Grudgeraker) are in general hard to avoid all ff with, and if a bad accident happens with the shotguns and you get a full load into your back, it hurts. Really the worst thing about Fireball and Hagbane is the DoT, though, as every tick distracts and if you’re shooting too (not really that rare) ruins your aim.
In general, I think the best way to learn the hazards of ff is to be the target in a tight situation a few times. Not on purpose, not as revenge or otherwise after the fact, but somehow notice how badly it affects the target and through that, the whole group. The Scoreboard Tweaks can help, and an additional indicator (both visual and aural) to the shooter could also help people notice when they actually hit someone, but the change has to start with the player.
The earlier debates about ff (especially before its damage nerf) indicate that both sides tend to blame the other. Targets blame the shooters for not aiming well, the shooters blame the target for moving in front of them. I have a strong suspicion that adding a significant penalty to the shooter would start the blame game again, and probably cause even worse revenge cycles than currently. So yeah, an indicator of some sort (visually, stronger than target reticule changing color or aurally, as the character saying “sorry”) could help a bit, but more than that would start wars.