To harbor evil intentions; to have ulterior motives that are hard to fathom.
他总是对新来的同事过分热情，让人觉得他居心叵测，不知道想从别人那里得到什么。
He is always overly enthusiastic towards new colleagues, making one feel he harbors ulterior motives, unsure of what he wants to gain from others.
Era:
Early Modern
Frequency:
Story:
During the Three Kingdoms period, Cao Cao planned to attack Sun Quan and Liu Bei. Fearing that Ma Teng of Liang Province might rebel, Cao Cao followed his advisor Xun You's suggestion: he offered Ma Teng the title of "General Who Conquers the South" and lured him to Xuchang, where he intended to kill him.
Ma Teng's nephew, Ma Dai, warned him that Cao Cao was a person with ulterior motives (居心叵测) and could not be trusted. However, Ma Teng did not heed the warning and went to Xuchang with his son Ma Xiu, only to be tragically killed by Cao Cao.
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