[1979. They went in to ‘teach Viet Nam a lesson’ and promptly got their butts kicked.]
https://en.m.wikipedia.org/wiki/Sino-Vietnamese_War
At Lang Son, they are said to have destroyed Vietnam’s Gold Star division, a seasoned regular (i.e. non-draftee) unit that saw action during the Vietnam War. In addition, they killed 100,000 Vietnamese civilians, if the Vietnamese government’s claims are to be believed.
https://www.historynet.com/war-of-the-dragons-the-sino-vietnamese-war-1979/
Then they shipped entire Soviet-built plants back to China at their leisure, without Vietnamese forces being able to interfere with their stately withdrawal, lest the incursion become a permanent occupation or even an outright annexation of the territory overrun.
* The Gold Star Division had run-ins with US forces in South Vietnam and had to be rebuilt from scratch, despite exaggerated Vietnamese claims of battlefield victories in the 60s, doubling or tripling the reported number of KIA inflicted on GIs in their area of operations as compared to the true numbers.
https://en.m.wikipedia.org/wiki/3rd_Division_(Vietnam)
https://en.m.wikipedia.org/wiki/Operation_Masher
I would be happy to believe you. So why is this not our?