Medium volume day trading (hundreds or thousands of transactions per day), where you make $500k per year (which will get you to the 40% marginal tax rate, 31% effective). Have to account for the basis of every trade, all short-term gains/losses, and let's assume they're doing that accounting work themselves (the hundreds of hours is a stretch though), and that they're not plugging a csv file into a program to take care of it for them so it's all manual gain/loss matching.
That's about as close as I could come without getting silly. Even oil companies like Exxon don't end up paying 40% (35% effective I think in their last fiscal year).
If you make $5+ million per year, and have nothing to offset any of that, you can end up paying over 40%. Pretty rare group of people likely to fall into that.