@lightingcloud
Looking at the raws, in the second frame Yuki-san starts using the term ore in the answer to a question. Ore is used by males. In third frame he uses Watashi, which is more formal and used mainly by females.
I had a feeling he said "ore" first, especially after mentioning he shouldn't use it in the previous chapter, and also because the mother misheard "au lait", which sounds somewhat similar to "ore" (to the Japanese at least).