You can actually do something similar to that in SMB1. Get a hacking utility (SMB Utility recommended) first. Since you can't really remove the block under the flag unless you start hacking deep in the code, you can do the next best thing: Remove the ground to the right of the flag for 2+ spaces. Mario will fall after touching the pole, and the game gets stuck in an unbreakable loop that hurts your ears. The same thing would probably happen if the block was removed from the bottom of the pole, and a pit was placed under it. I put it in the first level of my mario hack. Though kurtvegita's concept was pretty funny...
