Well, it depends. The general rule on this is that you need to make a profit in 3 out of 5 consecutive years ending with the year in question, unless the IRS proves otherwise. There are several exceptions to this rule, such as some farming and livestock activities. There is a special election form that can be filed in order to allow you more time to show a profit.
Various other factors go into determining whether you are engaged in a legitimate business endeavor. These are things such as the amount of time devoted to the business, having a business plan, having a marketing plan, and your overall income relative to the scale of the business. Confused yet?
We have had clients over the years who have legitimately deducted golfing, fishing, and other things as business expense.