My least favorite is a brown torso that breaks when you change the arms. I forgot old brown was so brittle, and felt really bad that I broke a nice chest piece. Light green Bionicle bones for the same reason, you can't build with them much before they break.
My favourite piece is the plate 2x3, because it is the best piece to build flowing landscapes.
There is no single "least favourite" for me, but a group: Any single-use part, especially the large ones. Like plane cockpits. Or many StarWars things. I just found a LEGO-car sized red dragons head while washing parts. WTF?
Eh, I'll give windscreens a pass, since there isn't a great way to do them using multiple smaller pieces, but that dragon head sounds inexcusable. C'mon LEGO, this is not f*cking playmobil. Assembly is the whole point!
I just found it is the head from Set 2507. Special moulded parts for one set, and then painted from several sides - must cost a fortune in production and development. For that money, they could have made a brick-built on.
With windscreens it is a mixed issue. Some have multiple uses, but some are not as good in that regard.
My favourite is 39793, the so-called 'biscuit', because it's really versatile and provides so many different connection opportunities. My least favourite is a bit more decisive, but it's probably part 15100, because it's way harder than it has any reason to be, to insert and remove from other pieces.
The Ornithopter set calls for putting that 15100 into two stacked 63782 after they’re held together with a 32062 and it is such a pain. I ended up doing it in a different order, getting the 15100 into one 63782, then the other, THEN putting the 32062 through them. Eventually though I realized the 15100 seats a lot easier if you twist it while pushing it though, and that made my life better.
The old "Reddish Brown" as of three or more years ago is know to be brittle. LEGO has changed to formula since which apparently fixed that.
Apart from your problem of getting the remains out, just contact LEGO support for free replacement parts, as this is a known and accepted issue. Keep the parts, though, if you ask for a larger number of parts, they might want the broken pieces back as proof (theoretically, I have nor heard of such a case personally).
I remember one of my elementary school teachers back in the 90s having a few, but even as a kid who got a lot of Lego sets I somehow never got one of my own
Until a couple of years ago, I'm now a grown ass adult, and my wife and I have been on a bit of a Lego kit, and just about every set we get seems to have one now.
So somewhere along the line Lego seems to have pivoted towards including more brick separators. I'm certainly not angry about that, but I definitely get how it could seem to some people that they're a mysterious new invention.
Basically my childhood, yup. But then again, the type of kits they let us use as kids seem to be more quantity than quality. Or maybe I was just poor, haha.
If memory serves that particular brown in recent manufacturing from Lego was known by the public over some time to have embrittlement issues, so probably not something you did to it, but something as of now that Lego has fixed on their end if you pick up that brown from a current set or from their stores.
The old brown from the 90s had the same problem; I've broken several while dismantling old used LEGO and it sucks. A lot of them were used in the old, kickass Pirate ships.
I have the complete shell of that pirate ship and the body is still very strong. All the brown accessories however (muskets, barrels, etc) turned to dust long ago.
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