(Romaji: "sugokatta desu!"; English: "It was awesome!")
So, right before today's Linear Algebra exam, I went up to the whiteboard and wrote 「がんばりましょう、みなさん」(Romaji: "ganbarimashou, mina-san!"; English: "Let's do our best, everyone!") and I guess the class was in a bit of an Asian mood or something because we were able to coerce another student into writing it in Korean, and another to do the same in Vietnamese, though he ran out of time before the professor came in so it was just the Japanese and Korean there.
The professor looked puzzled as he walked in, and after we explained the writings to him, he chuckled and agreed. He decided to leave them up there for the duration of the exam. :)
楽しかったですよ…
(Romaji: "tanoshikatta desu yo..."; English: "It was quite fun...")
[Edit: Fixed adjective inflections, thanks to
katoriina_san.]