I witnessed that happened one time to my wife (btw a Chinese) as we left a department store and were going to the bus stop. One of among four of the drunken lout brethren grabbed her rear. ...
Happened to my (now ex-) wife in the bazaar in Istanbul. She hit him, hard, and he took off. I disentangled myself from the two-year-old and pursued. At the time, I was about 30 and in fair shape. He was fatter & older, so I caught him, cornered him in the doorway of a closed shop. I was going to clobber him, but then I realised there were about a dozen young men right at my shoulder, so I limited my action to telling him off, unfortunately in English since I did not speak Turkish.
One of the young men translated, then several of them yelled at him. He was quivering, almost in tears. My wife arrived, carrying the kid, and joined in.
He then fled again. When we lost sight of him, he was running through the bazaar head down and hands up to shield his face, with half a dozen young men running alongside and beating on him. I think it was mostly for show; they did not trip him and really pound him and they were using the side of the fist not punching. However, they were definitely not being gentle either.
I wonder how a Chinese crowd would respond in that situation.