Why do people always laugh when I say I boycott Wal-Mart?

It happened again this morning, as it has happened countless times--someone asked me if I had seen the lines at Wal-Mart, and I said no, I've boycotted Wal-Mart for many years, and someone standing nearby began laughing. As always, I asked "Why is that funny? They do terrible things to people." And as always, the laugher said "I know they do; I've read quite a lot about it."

So could someone please let me in on the joke?