"Ching, ching, ching"

Incident occurred in October 2016: 

I was walking to the YMCA when a group of high school boys muttered "ching, ching, ching" under their breath, but just loud enough for me to hear. They were giggling. At this particular Y, there are a lot of Chinese speaking members, many of whom don't speak English. I guess these boys assumed I didn't speak English and wouldn't catch on to their blatant racism.