I believe the fastest way to get a "love letter" from the IRS is to ignore your gambling "winnings" when you file your tax return. I know what you're thinking. It's either "they already withheld taxes at the casino, so that took care of it" or "I lost more than I won, so that means I don't have to report it". Wrong and wrong.
The saddest example of this that I've seen was a fellow who came in my office one day to see if he needed to file a tax return. He was single, 72 years old, and living on a $800 monthly pension and his social security. I asked him all the usual questions, and all I could get out of him was a statement from his bank showing he had earned $0.37 in interest on his savings account for the year. He specifically said he had no gambling winnings. So I told him his pension was below the limit for needing to file a tax return, and at his income level his social security wasn't taxable.
Several months passed before I saw him again, this time red faced, beyond angry, and clutching an IRS letter saying he owed them over $3,100 because he didn't file his tax return. Of course, I was guilty until proven innocent.