upstart

 Longman Dictionary of Contemporary English 5++朗文当代英语 5++LDOCE 5++朗文 5++up·start /ˈʌpstɑːt $ -ɑːrt/ noun [countable]  BOASTsomeone who behaves as if they were more important than they really are and who shows a lack of respect towards people who are more experienced or older 目中无人的新人[年轻人]；自命不凡的家伙 a cheeky young upstart 一个无礼的后生小子 —upstart adjective

Examples from the Corpus

upstart• We made suggestions, to be overruled by upstarts.• She certainly hoped Albert didn't let in any little upstarts like the officer who'd wanted her apartment!• Well, she wasn't about to let this little upstart have her home.• These upstarts are beating us at our own game, manufacturing and marketing.Origin upstart (1500-1600) upstart “to jump up suddenly” ((14-19 centuries))

up·start nounChineseSyllable  

Corpus as they behaves were someone if who

upstart
up‧start /ˈʌpstɑːt $ -ɑːrt/ noun [countable]someone who behaves as if they were more important than they really are and who shows a lack of respect towards people who are more experienced or older:
    a cheeky young upstart
—upstart adjective

up·startBrE /ˈʌpstɑːt/ 🔊NAmE /ˈʌpstɑːrt/ 🔊 noun (disapproving) a person who has just started in a new position or job but who behaves as if they are more important than other people, in a way that is annoying 自命不凡的新上任者；狂妄自大的新手