Near Christmas the offices in Europe has Christmas jumper day. Is it allowed to wear something like Christmas jumper? I know it’s just a jumper but the fact it is “Christmas” and sort of participate in it by wearing it.
There are two issues that might arise:
Imitating non-Muslims. I asked a relevant question here: How to distinguish "imitation" from "doing the same thing"? There's not a clearly identifiable boundary between "imitation" and "doing the same thing".
Images of living beings (tasweer). See e.g. Ahadith Concerning Taswir (Pictures) for a list of relevant ahadith.
This is going to be one of these borderline issues, too specific to have a precise ruling (and it will depend on exactly what's on the jumper). More devout Muslims would likely avoid the issue entirely.
It is not haram but it is not good thing either If your intentions are to just have fun or entertainment then it is o.k but christmas stories are creates from the christian perspective that may be not true according to islamic perspective. For example:in islam jesus was not son of god but in christianity he was. In islam he was not crucified but in christianity he was. Therefore,It is better to avoid the clothings and religious ceremonies of other religions that may present the distorted views about reality according to islamic point of view.