Fairly easily actually. Have you ever, in your entire life, actually spoken up against racism? Have you been racist towards anyone yourself and made excuses for your actions instead of owning it? If somebody behaved in a racist way towards someone, would you say/do something about it?

To be extremely clear, I'm not saying you have some kind of duty to do any of this or that you're necessarily a terrible person if you haven't. But if you've never made any meaningful effort to oppose racism, if your level of caring doesn't ever reach the point of some kind of action, I'd say you're not what anyone would call "anti-racist."

It's not about screaming at the top of your lungs. Most of the idiots who do stuff like that aren't really anti racism either. It's about sincerity.