Nut up or shut up

Every evening after Wild Man goes to bed, PW and I watch a little TV, generally while we do various other things around the house or work. In the past few weeks we've seen a lot of commercials for Woody Harrelson's new movie Zombieland. Most of the trailers have included what is apparently Harrelson's character's catch phrase in the film: "Nut up or shut up." Last night, as I was prepping for today's class, PW was watching a football game. And again, we saw a trailer for the movie. This time, however, the catch phrase was changed to "Put up or shut up," and the change had clearly been looped in. It was a very, very noticeable change. Since then I've been wondering what is so offensive about the original phrase that it had to be changed. Is this only an American issue? Last night we were watching an American channel, and we'd always seen the trailers on Canadian channels previously. Why the change? In what rhetorical situation is this particular phrase inappropriate or worthy of censoring?