The foreign ministry said if Mr Trump was confrontational, it "must really be diagnosed as the relapse of the dotage of a dotard".
The Oxford English Dictionary defines a dotard as "a person whose mental faculties are impaired, specifically, a person whose intellect or understanding is impaired in old age".
Dotage, meanwhile, is defined as "having impaired intellect or understanding in old age", or in general use as "old age".
At the Nato summit in the UK on Tuesday, Mr Trump referred to North Korean leader Kim Jong-un as "rocket man".
He also said that the US reserved the right to use military force against Pyongyang.