There was one black female mentee who I noticed was timid in taking credit for her work. I had recently attended a diversity panel where someone in a similar role as me said that in a similar situation, and her advice to her mentee was "Think about what a white man would do" and everyone applaud such an insightful advice. So identifying such an opportunity, I said the exact same thing word for word, basically "I see you're hesitating to take credit for your work. Think about what a white man would do."
Immediately after saying that, I could tell it wasn't taken well, and she asked "what does that mean?" I couldn't come up with an answer for that which wouldn't be taken in a really bad way, so I backpedaled. She later reported me to an administrative person who luckily felt it was too vague to file a serious report about, but told me to watch what I say.
But I do have a solution (my trick). From that point on, I definitely give more subtle advice unless they have passed my test, which is I see how they react to situations where they could give the benefit of the doubt to others in vague situations. Sometimes, I'll bring up a past story about another anonymous person and see if they are outraged and want to get them in trouble. Only the ones who remark that they probably had good intentions, and don't react too strongly, I'll give more candid advice to.
Even if "what a white man would do" wasn't emotionally charged (and it is), it's not a good way to make the point.
Look at how often people tweak, clarify, and edit their comments even here on hacker news. So you'll probably just end up with "stifled" advice (using the terminology from the article), as you can see with all these suggestions in this thread.
If I was giving advice to someone who was too assertive and taking too much credit, I would never say "Think about what a black woman would do." Things like this are so transparently racist it shouldn't even need to be explained. You are simultaneously characterizing a race and gender of people and also telling someone else to act like a different race and gender.
The reason the advice was poorly received is because it is nonsense. The recipient of the advice asked the perfect question - "what does it mean to act like a white man?" The OP, when asked, also doesn't seem to know what it means. I'd say there is a lesson there - don't repeat something just because it was will received when you originally heard it. You may not understand it. It may be something of an emperor's new clothes situation where nobody can question the person who gave the original advice, but that doesn't make it good.