n.someone who is unimportant but cheeky and presumptuous
同义词：jackanapeslightweight
英汉双解大词典
whippersnapper/ˈwɪpəˌsnæpə/(whippersnappers)
1.
N-COUNT（可数名词）
If you refer to a young person as a whippersnapper, you disapprove of them because you think that they are behaving more confidently than they should. 妄自尊大的人 [非正式，老式]