"Ask me how I know" is a rhetorical question that means "I speak from personal experience". It is not an actual invitation to ask, because the answer is already

"Ask me how I know" is a rhetorical question that means "I speak from personal experience". It is not an actual invitation to ask, because the answer is already implicit in the question. In this case, It happened to me and I saw the same happen to several coworkers as well.