The first thing you really need to understand is that the definition of racism that you probably have (which is the colloquial definition: “racism is prejudice against someone based on their skin color or ethnicity”) is NOT the definition that’s commonly used in anti-racist circles.
The definition used in anti-racist circles is the accepted sociological definition (which is commonly used in academic research, and has been used for more than a decade now): "racism is prejudice plus power". What this means, in easy language:
A. Anyone can hold “racial prejudice” — that is, they can carry positive or negative stereotypes of others based on racial characteristics. For example, a white person thinking all Asians are smart, or all black people are criminals; or a Chinese person thinking Japanese people are untrustworthy; or what-have-you. ANYONE, of any race, can have racial prejudices.
D. People of color can be prejudiced, but they cannot be racist, because they don’t have the institutional power. (However, some people refer to intra-PoC prejudice as “lateral racism”. You may also hear the term “colorism”, which refers to lighter-skinned PoC being prejudiced toward darker-skinned PoC.) However, that situation can be different in other countries; for example, a Japanese person in Japan can be racist against others, because the Japanese have the institutional power there. But in North America, Japanese peoplecan’t be racist because they don’t hold the institutional power.
E. If you’re in an area of your city/state/province that is predominantly populated by PoC and, as a white person, you get harassed because of your skin color, it’s still not racism, even though you’re in a PoC-dominated area. The fact is, even though they’re the majority population in that area, they still lack the institutional power. They don’t have their own special PoC-dominated police force for that area. They don’t have their own special PoC-dominated courts in that area. The state/province and national media are still not dominated by PoC. Even though they have a large population in that particular area, they still lack the institutional power overall.
F. So that’s the definition of racism that you’re likely to encounter. If you start talking about “reverse racism” you’re going to either get insulted or laughed at, because it isn’t possible under that definition; PoC don’t have the power in North America, so by definition, they can’t be racist. Crying “reverse racism!” is like waving a Clueless White Person Badge around.