The challenge starts with a notabug post, with the goal of finding out information about domay1986. The list of posts contains 2 that are relevant:

1. Is HackerNews any good? suggests a visit to Hackernews. A quick visit finds this profile, with his first name: Eugene.
2. In defense of the "selfish" baby boomers points toward Facebook. Searching up Eugene 1986 on FaceBook finds this profile. The Romanian references tell us this is what we are looking for.
3. The FaceBook post contains a link back to the xmas ctf website. Using the standard SQL injection ' or true or ', we get access to a fictional medical record with his address, blood type and height.
4. A search with the address reveals that Domay lives in Scranton (where the Office was filmed). The blood type was 0-.
5. Back on the FaceBook page, the xkcd screenshot contains unclosed tabs. One of them has title Matrimoniale, and we find a Romanian dating website with Domay’s profile, revealing his favorite color: magenta.

The key was X-MAS{eugene_clarke_scranton_magenta_0-_162}.