Just adding, the literal meaning is "to be taught less (by someone parents/guardian)". kurang = less/deficient, ajar = teach Back then when someone have bad manners or habits, people assume that it's because of their parents didn't teach him/her properly. Nowadays this phrase is not as harsh as it was before. It's so frequently used and people even use it when joking. So, depending on the situation it could mean "insolent", "rude", "disrespectful", "impudent", "impertinent", "atrocious", "discourteous" in its literal serious meaning or just "You jerk!", "Damn!", "Shit!" in less serious situation or jokingly said.

Kurang Ajar means - Rude - No manner - Insolent - Impudent

kurang ajar means impolite or rude.

DavidXian explain the phrase clearly but for me "kurang ajar" it's more close to "impolite"

kurang ajar = 没有家教 = 没有规矩 = 没有礼貌