Fragmenting or non-sticking decals, especially when they are of a type you don't have in your spares box (and
it seems like they always are
) are definitely my most hated "feature".
If the decals are from a 30-year-old Airfix or Frog kit, well, that's just one of the things you have to put up
with if you build old, second-hand kits like I do - however, there are a number of newer kits, including some produced in the last few years, which STILL have this sort of problem.
The worst offender seems to be Roden (who mostly produce 1/72 WW1 aircraft). Roden's kits are very finely-moulded and
detailed, and they make a huge range of interesting aircraft types - however the decals are very prone to breaking up, to
say the least! I recently build their Felixstowe flying boat and the decals for that (thankfully I tested one of the alternative-scheme decals first) disintegrated into small fragments the moment I tried to slide them off. After several
coats of spray-on varnish, they went on OK - but this sort of thing is unacceptable for a modern kit, released in the last few years and costing over £20 new.