Shirtless and watching replays of himself on television, apparently.
There was a 50-minute rain delay in Rafael Nadal's easy 6-2, 6-2, 6-1 over David Ferrer in Friday's French Open semifinal. Television cameras captured how Nadal spent his break.
That's Rafa's Uncle Toni, giving him coaching tips. So, pretty much, there's not a lot of difference between a match and a mid-match break.