向(む)きになるto become serious, to take something seriously (joke, teasing), to become irritated or angry (usu. at something trivial), to get worked up

ちょっと、向(む)きになって突(つ)っかからないで！

Hey, don't get worked up and start a fight! {to become serious, to take something seriously (joke, teasing), to become irritated or angry (usu. at something trivial), to get worked up}

ムキになって怒(おこ)っている親友(しんゆう)が面倒臭(めんどうくさ)いです。

My best friend, who gets seriously angry over trivial things, is being annoying. {to become serious, to take something seriously (joke, teasing), to become irritated or angry (usu. at something trivial), to get worked up}

野球(やきゅう)好(ず)きの父(ちち)は、野球(やきゅう)の話(はなし)になると向(む)きになります。

My father, who loves baseball, becomes serious whenever the conversation turns to baseball. {to become serious, to take something seriously (joke, teasing), to become irritated or angry (usu. at something trivial), to get worked up}

からかっただけでムキになって怒(おこ)る彼女(かのじょ)は扱(あつか)いが難(むずか)しいです。

She gets seriously angry and worked up just from being teased, making her difficult to handle. {to become serious, to take something seriously (joke, teasing), to become irritated or angry (usu. at something trivial), to get worked up}

友達(ともだち)：「おい。さっきの発言(はつげん)は冗談(じょうだん)だったって！そうムキになるなよ！」

Friend: "Hey. That comment earlier was just a joke! Don't take it so seriously!" {to become serious, to take something seriously (joke, teasing), to become irritated or angry (usu. at something trivial), to get worked up}