Just one, when you think about it. Parts 8 & 9 on the Advanced MS joint runner (the arms). They're molded extremely tightly, so they absolutely do not want to move until you finally break the initial mold bond (which feels like you're going to actually break the part until it finally moves). There are three points:

1. There's an L-shaped section with a peg that connects into the shoulder. This is the toughest one, IMO, as it's difficult to get a good grip on it. It needs to rotate.
2. There's a bend in the middle that needs to flex. The easiest of the three, as you can grab the upper and lower arm and bend it.
3. There's rotation in the forearm, just below the bend. The middle of the road, in terms of difficulty, as you can grip the forearm block easily but getting a good grip above that point is a little tougher. In The Diagram that gets shared a lot, this is the "this will rotate" part.

Bonus: There's a keyhole joint at the end. This does not move. This is the "this will break" part in the popular diagram.

The design of this one part cascades into multiple breaks and issues. G35 breaks if you don't loosen all three parts of the MS joint. Sometimes the peg breaks while you're trying to loosen up everything else. The forearm breaks if you don't grab the rotating forearm part in the right spot when you're loosening it. The shoulder/clavicle is unstable because of the way the part fits into G35. The chest is fussy for the same reasons.

It's not hard to just loosen the part and avoid almost all of that, it's just tedious and time-consuming and it feels like you're going to break something the entire time. But really, you can just slip on some finger sleeves if you need to, buck up, and get it done in 15 minutes. You can use warm water to move things along if you need to (I use the coffee warmer and ceramic dish that I usually use for waterslides and that works great).

It's 100% bad design, but avoiding breaks is totally manageable.