Well it doesn't change the broadcast rating as long as they're censored, so there would be no hard and fast restriction, but WWE likes to maintain as close to constant PG as they can get so that they can sell the entire product as PG.
Has anyone dropped anything worse than an "ass" though?
--
Thank you, Eddie Guerrero.
http://www.wwe.com/f/styles/photo_large/public/photo/image/2012/04/33_Moscow_04112012jg_02128.jpg