I just went on a ride and didn't wear my FF. That's really rare but my head said it was an exploratory ride so I wouldn't be going for Adrenalin. As Gary said. You just have to decide based on what YOU ARE DOING but never decide on WHAT YOU THINK PEOPLE WILL THINK.
For ribs, wearing armour WILL NOT ! (yes, I'm shouting

) guarantee you won't break your ribs. The way falls happen and the way ribs branch out means they can break unless you wear a full exo-skeleton - which no one does - and even then you could in theory still break them. Armour doesn't stop injuries, it reduces them.
For ribs, I've broken mine 4 times now in just over 2 years. 3 on the bike and one young horse kicking me six meters in the back. That was the worst by far. Back rib breaks are horrible. Twice on the bike were unarmoured. Once armoured.
@High Rock Ruti has also broken ribs even when heavily armoured, I'm sure there are many more.
There's quite a good body armour thread and lots of other info in the reviews area. Body armour is all a compromise. There is no perfect armour. It's about picking something which works for you which you're more likely to wear than not wear. You could have the best armour in the world, but if you hardly wear it because it's hot, uncomfortable, restrictive, difficult to put on/take off, you feel like robocop - then it's pointless having it. Better to have a lesser armour you wear more frequently than an amazing armour which sits in the wardrobe.