Not an IPO but I was hired by a company that was supposed to extend me an offer including stock options, unfortunately there was miscommunication about shares vs options, netting me 1/100th of what I expected. I was so angry I seriously considered taking a short position against the original amount of stock I was promised, but in the end it just didn't feel right to bet against my employer. A year later and their stock had dropped from $43 to 50 cents which would have netted a huge windfall. The money would have been nice but I don't regret standing on principle.