I had to do one of these lists, being so close to graduating with this major. Feel free to contribute in the comments, and I may include it later on.
So, you know you’re a Japanese major when:
-you’re trying to learn Japanese and you end up learning some English word that you never knew instead (i.e. 無口=taciturn).
-you start using English phrases that you never used before learning Japanese (i.e. “I’ll do my best!”).
-あの is officially a word in your vocabulary.
-you study abroad in Japan in a supposed attempt to learn Japanese but end up either:
1. trying to talk to Japanese people in Japanese but ending up helping their English instead.
2. hanging out mostly with the other study abroad students instead of Japanese students.
-you think it is all about Japanese language, and then you have 5 literature classes that you have to take.
Hope to make this list longer in the future. Add some comments with suggestions, and I’ll consider them for an update.