質問: こんばんは! I've taken the challenge to try to read a book written in japanese, and it's been pretty hard, but I'm learning a lot. I haven't been able to figure out the meaning of the following: ついかっとなってしまう Specifically, the 『ついかっと」part. 読んでくれてありがとう!
回答: You are parsing the phrase incorrectly, which is preventing you from looking up the words in the dictionary. 「つい」 means "carelessly", "inadvertently", "by chance", "in spite of oneself", etc. 「かっとなる」 means "to flare up", "to lose one's temper", etc. Thus, 「ついかっとなってしまう」 means: ***"I (or someone) lose(s) my/his/her temper in spite of my/him/herself."***