The fact that Einstein and Wittgenstein held more prestigious positions at other points in their lives would not have spared them from an attitude like the OP demonstrated at the time they held the more menial jobs, and judging only by those menial jobs.
Who knows what heights of glory this particular Target employee will climb to in the future? History is even more full of people who once held menial jobs but then went on to achieve vast fame and fortune (and perhaps even be judged a "genius" by many).
We also don't know what this particular Target employee did before he worked at target and taught LSAT courses. Perhaps, like Wittgenstein, he'd been a lecturer at Cambridge and was awarded some prestigious degree.
Ok, I know that's stretching credibility. He probably wasn't. But my point is that we don't know his past or his future. All we know are two job titles and his boast of being a genius. Should we judge him based on just those couple of facts? Or should we withhold judgment? My vote is for the latter.
Finally, I never claimed that Einstein or Wittgenstein weren't recognized during their lifetimes, just that Kafka and Van Gogh weren't, and that many others who are generally considered "geniuses" now weren't either.