This may sound silly at first, but it is an essential loafing strategy. If you are planning on goofing off all day, get to the office way early. Trust us. If business hours start at 8 a.m., arrive at 7 a.m. Yes, we know. That does sound idiotic. Let us finish.
Once you arrive, find an email or two that you can quickly reply to that lets your boss or client know that you were working on stuff before business hours. That email provides a timestamp, the corporate America version of Willy Wonka's golden ticket. Tales of your heroism will be spoken in hushed tones by the water cooler. Your co-workers will be in awe of you. After you send those couple emails, do no other work. Read Twitter. Take a nap. Try to beat that 6-second high-score in Minesweeper. It doesn't matter what you do during that time, but don't do any more work until your supervisor arrives. They will be so impressed with your commitment that they'll cut you some slack to slack even more.