Interview Question for Software Engineer at Garmin:

Tell them to go on diet.
But more seriously, first talk to them and find out if there is some issue in their personal life that is affecting their work (you don't need to know what the issue is, just that its there) and see if you can help (with the work load). If they are just being lazy or are incompetent, and its affecting you or your work, then don't get emotional, angry, slanderous etc. You need to be professional, calm and straight forward and open, and most importantly, document everything. By document, I mean that you e-mail the person and cc at least 2 managers BEFORE the pumpkin hits the fan while the co-worker still has time to haul his fat out of the fire. When the finger pointing starts, you want to be able to print out at least 4 or 5 emails going back days and weeks warning of this very thing. Avoid back stabbing and charged emotions.