Definition
To behave in a dishonest or mischievous way; to be engaged in activities that are not good or are likely to cause trouble.
行爲不端；做不正當或不誠實的事
The group of teenagers was loitering suspiciously on the street corner, looking like they were up to no good.
那群青少年在街角可疑地徘徊，看起來像是要做壞事。
He's always sneaking around; I suspect he's up to no good.
他總是鬼鬼祟祟的；我懷疑他沒安好心。
She found her son sneaking out of the house in the middle of the night; he must be up to no good.
她發現她兒子半夜偷偷溜出房子；他肯定沒幹好事。