These jeans are […], you need to iron it.
After the washing machine, the clothes are […]. You have to iron them.
What adjective would you fill in the gaps with? My dictionary gives me wrinkled, creased, rumpled, and crumpled.
There's quite a lot of regional variation on this one, but here's the overall picture
I won't bother adding more charts, but if you follow the link above, and toggle between US/UK corpuses, you'll see that Brits still favour crumpled, but Americans have moved decisively in favour of wrinkled over recent decades. By weight of numbers wrinkled is definitely the one with the most promising future.
In the context of clothes, wrinkled, crumpled, creased, rumpled, etc. all mean exactly the same thing. But note that trousers, for example, may occasionally be approvingly referred to as nicely creased when they've been ironed/pressed to make a sharp fold line exactly where it's wanted.
Based on Skymninge's response, there may be some UK/US difference here.
In the US, the word you are looking for would clearly be "wrinkled". In general:
"Wrinkled" means having undesired, unordered lines, folds, or ridges in the material.
"Crumpled" means not neatly folded or hung, like if you just threw them on the floor.
"Creased" can refer to any folds or ridges in the material, but is usually used to refer to a desired ridge. On pants, that would be the creases down the front and back of the legs.
"Rumpled" is generally irregular and untidy. I think it's a somewhat out-of-date word.
Wrinkled is more used for wrinkles on skin, crumpled is used for "crumpled look" clothing (clothes that are meant to look unironed), so this is the one you're searching for.